Original Article

Iatrogenic Bone and Soft Tissue Trauma in Robotic-Arm Assisted

Total Knee Arthroplasty Compared With Conventional Jig-Based

Total Knee Arthroplasty: A Prospective Cohort Study and

Validation of a New Classification System

Babar Kayani, MRCS, MBBS, BSc (Hons) a, b, *,Sujith Konan, MBBS, MD (Res), FRCS (Tr & Orth) a, b,Jurek R.T. Pietrzak, MB BCh, FCS(SA)Orth a, b,Fares S. Haddad, FRCS (Ed), Dip Sports Med, FFSEM a, b

a Department of Trauma and Orthopaedics, University College Hospital, London, United Kingdomb Department of Trauma and Orthopaedics, Princess Grace Hospital, London, United Kingdom

a r t i c l e i n f o

Article history:

Received 15 January 2018

Received in revised form

9 March 2018

Accepted 15 March 2018

Available online xxx

Keywords:

bone trauma

classification

robotic surgery

soft tissue injury

total knee arthroplasty

a b s t r a c t

Background: The objective of this study was to compare macroscopic bone and soft tissue injury between

robotic-arm assisted total knee arthroplasty (RA-TKA) and conventional jig-based total knee arthroplasty

(CJ-TKA) and create a validated classification system for reporting iatrogenic bone and periarticular soft

tissue injury after TKA.

Methods: This study included 30 consecutive CJ-TKAs followed by 30 consecutive RA-TKAs performed by

a single surgeon. Intraoperative photographs of the femur, tibia, and periarticular soft tissues were taken

before implantation of prostheses. Using these outcomes, the macroscopic soft tissue injury (MASTI)

classification system was developed to grade iatrogenic bone and soft tissue injuries. Interobserver and

Intraobserver validity of the proposed classification system was assessed.

Results: Patients undergoing RA-TKA had reduced medial soft tissue injury in both passively correctible

(P < .05) and noncorrectible varus deformities (P < .05); more pristine femoral (P < .05) and tibial

(P < .05) bone resection cuts; and improved MASTI scores compared to CJ-TKA (P < .05). There was high

interobserver (intraclass correlation coefficient 0.92 [95% confidence interval: 0.88-0.96], P < .05)

and intraobserver agreement (intraclass correlation coefficient 0.94 [95% confidence interval: 0.92-0.97],

P < .05) of the proposed MASTI classification system.

Conclusion: There is reduced bone and periarticular soft tissue injury in patients undergoing RA-TKA

compared to CJ-TKA. The proposed MASTI classification system is a reproducible grading scheme for

describing iatrogenic bone and soft tissue injury in TKA.

Clinical Relevance: RA-TKA is associated with reduced bone and soft tissue injury compared with con-

ventional jig-based TKA. The proposed MASTI classification may facilitate further research correlating

macroscopic soft tissue injury during TKA to long-term clinical and functional outcomes.

© 2018 Elsevier Inc. All rights reserved.

Total knee arthroplasty (TKA) is an established and highly

effective treatment for end-stage knee osteoarthritis. The proced-

ure is performed in over 90,000 patients per year within the United

Kingdom [1]. The technical objectives of surgery are to replace

diseased bone with artificial implants, restore alignment, preserve

the joint line, balance flexion and extension gaps, and maintain the

normal Q angle for patella tracking. To achieve these objectives,

preservation of the surrounding soft tissue envelope during TKA is

essential [2e7]. Inadvertent injury to the periarticular soft tissue

structures such as the collateral ligaments, posterior cruciate

One or more of the authors of this paper have disclosed potential or pertinent

conflicts of interest, which may include receipt of payment, either direct or indirect,

institutional support, or association with an entity in the biomedical field which

may be perceived to have potential conflict of interest with this work. For full

disclosure statements refer to https://doi.org/10.1016/j.arth.2018.03.042.

* Reprint requests: Babar Kayani, BSc (Hons), MRCS, MBBS, Department of

Trauma and Orthopaedics, University College London Hospital, 235 Euston Road,

Bloomsbury, London NW1 2BU, United Kingdom.

Contents lists available at ScienceDirect

The Journal of Arthroplasty

journal homepage: www.arthroplastyjournal .org

https://doi.org/10.1016/j.arth.2018.03.042

0883-5403/© 2018 Elsevier Inc. All rights reserved.

The Journal of Arthroplasty xxx (2018) 1e6

ligament (PCL), or extensor mechanism may compromise post-

operative clinical and functional recovery, reduce stability, and

decrease implant survivorship [2,6e8].

In patients undergoing conventional jig-based total knee

arthroplasty (CJ-TKA), correct alignment and soft tissue tensioning

may be achieved using a measured resection technique or gap-

balancing technique [9e12]. Bone resection is undertaken using

intramedullary or extramedullary alignment guideswith amanually

controlled oscillating saw blade. Surgical instruments are often used

to protect supporting ligamentous and neurovascular structures.

Controlled selective or more aggressive soft tissue releases may be

used to balance flexion and extensions gaps. However, manual error

associated with inadvertent soft tissue release during preparation

for implantation or tissue damage from the sawblade is an accepted

risk of the procedure. In many cases, this subtle soft tissue injury is

unnoticed or under-reported [13e19] and its long-term clinical and

functional significance remains undetermined [19].

Recent advances in surgical technology have led to the devel-

opment of robotic-arm assisted total knee arthroplasty (RA-TKA).

This uses preoperative computerized tomography scans to create a

patient-specific computer-aided design model of the knee joint.

The surgeon uses this virtual 3-dimensional model to create a

surgical plan for the desired bone coverage and limb alignment.

Computer software calculates the optimal bone resection window

and implant positioning for implementation of this plan, and an

intraoperative robotic arm helps to execute this surgical planwith a

high level of accuracy. Bone resection is limited to within the

stereotactic boundaries of the predefined haptic bone window,

which conceptually helps to limit bone and periarticular soft tissue

injury [20]. To our knowledge, there are no existing clinical studies

comparing bone and periarticular soft tissue injury in CJ-TKA vs

RA-TKA and no existing classification systems for grading peri-

articular soft tissue injury in TKA. A validated grading systemwould

help to standardize reporting of bone and soft tissue injury during

TKA and facilitate future studies exploring the impact of bone and

periarticular soft tissue injury on long-term clinical outcomes and

implant survivorship.

The primary objective of this study was to compare intra-

operative bone and soft tissue injury in CJ-TKA vs RA-TKA. We

hypothesized that patients undergoing RA-TKA would have

reduced iatrogenic bone and soft tissue injury compared with

CJ-TKA due to the presence of stereotactic boundaries with robotic-

guided surgery. The secondary objective was to develop a validated

classification system for documenting and researching intra-

operative bone and soft tissue injury during knee arthroplasty.

Materials and Methods

Patient Selection

This prospective cohort study included 60 patients with symp-

tomatic knee osteoarthritis undergoing primary TKA between

January 2016 and July 2017. This included 30 consecutive RA-TKAs

and the preceding 30 consecutive CJ-TKAs before robotic-assisted

TKA was fully introduced into the unit. The treatment group allo-

cated to each patient was decided by the date of the surgery with

operative procedures before September 2016 undergoing CJ-TKA

and operative procedures after this date undergoing RA-TKA. All

operative procedures were performed by the senior author (FSH)

who is fully trained in CJ-TKA and has previously undergone

cadaveric training in RA-TKA. The inclusion criteria for the study

included: patients with knee osteoarthritis; patients greater than

18 years of age; both surgeon and patient agree that TKA is themost

suitable treatment; patient is fit for surgery following review by an

anesthetist and surgeon; patient has surgery performed using

either CJ-TKA or RA-TKA. The exclusion criteria included the

following: patient is unwilling to participate in the study; patient

has diagnosis of inflammatory arthropathy or collagen disorders;

patient undergoing revision TKA for failed unicompartmental

arthroplasty or tibial osteotomy; and patient has surgery per-

formed using an alternative surgical technique (eg, computer

navigation). Written informed consent was obtained from all pa-

tients included in this study. The proposed study was prospectively

reviewed by the hospital board who confirmed further institutional

research ethics board review was not required.

Preoperative Clinical and Radiological Data

Baseline characteristics relating to age, gender, bodymass index,

American Society of Anesthesiologists grade, laterality of surgery,

preoperative range of movement, and varus or valgus alignment

with degree of passive correction were prospectively recorded for

each patient. Patients in both study groups had preoperative

anteroposterior and lateral weight-bearing radiographs. In all

patients undergoing RA-TKA, an additional CT scan of the knee joint

was performed. This was used to create a patient-specific

3-dimensional model of the patient's native knee anatomy and

computer software was used to plan optimal bone resection and

implant positioning for the desired bone coverage and limb

alignment.

Surgical Technique

In both treatment groups, a tourniquet was applied but not

inflated unless there were intraoperative concerns regarding he-

mostasis or obtaining a satisfactory bone-cement interface. A

midline skin incision with medial parapatellar approach was used

with preservation of a 3-mm cuff of quadriceps tendon attached to

vastusmedialis and a cuff ofmedial retinaculum to the patella to aid

closure. The anteromedial capsule was released subperiosteally off

the proximal tibia, patella everted, retropatellar fat pad excised, and

anterior cruciate ligament resected. Medical and lateral menisci

were excised, and osteophytes were removed using a bone nibbler

and broad osteotome. In patients undergoing CJ-TKA, extra-

medullary referencing was used to perform the tibial bone resec-

tion. An oscillating sawblade and cutting block were positioned to

perform the tibial resection perpendicular to the anatomical axis of

the tibia in the coronal plan with an anteroposterior slope of 3! in

the sagittal plane. Intramedullary referencing was used for the

femoral resectionwith avalgus angle of 5-9 degrees as guidedby the

preoperative imaging. Blunt Hohmann retractors were used to

protect the soft tissues throughout. Following this, soft tissue re-

leases were performed as required to ensure satisfactory balance of

flexion and extension gaps. All soft tissue releases were recorded. In

patients undergoing RA-TKA, femoral and tibial registration pins

were inserted for the attachment of the femoral and tibial arrays,

and the surgeon-controlled robotic arm was used to execute the

planned bone cuts and guide implant positioning. The robotic arm

had visual, auditory, and tactile feedback to ensure accurate bone

resectionwithin the stereotactic window and limit sawblade action

outside of this field. The degree of accuracy for RA-TKA is 2 degrees/

2 mm. Intraoperative dynamic referencing was used to assess on-

table alignment, stability, and range of motion with live on-screen

measurements. In both groups, the PCL was incised and later

removed with the box cut.

The implants used in both groups were the Triathlon Posterior

stabilized (PS) implant (Stryker, Mahwah, NJ) which consists of a

Triathlon PS femoral component, universal baseplate tibial

component, and polyethylene insert. Patella resurfacing was per-

formed in both treatment groups.

B. Kayani et al. / The Journal of Arthroplasty xxx (2018) 1e62

Baseline Characteristics

There were no differences in baseline characteristics between

the 2 treatment groups in relation to age, gender, body mass index,

American Society of Anesthesiologists score, laterality of surgery,

and preoperative coronal or sagittal plane deformities (Table 1).

Two patients in the CJ-TKA group had coronal deformities that were

not passively correctible. There was no statistical difference in

correctability of coronal plane deformities between the 2 treatment

groups.

Intraoperative Clinical Photographs

Standardized intraoperative photographs with a 100-mm lens

(EF 100 mm f/2.8 L Macro IS USM, Canon Inc., Ohta-ku, Tokyo,

Japan) were obtained following femoral and tibial bone preparation

to assess the iatrogenic bone and soft tissue injury. Five photo-

graphs were taken in each patient to assess the soft tissue condition

within the medial, lateral, anterior (extensor mechanism), and

posterior compartments. All photographs were taken from 1 meter

to enable accurate and clear visualization of the bone and peri-

articular soft tissues whilst ensuring that the sterile surgical envi-

ronment was not compromised. Six blinded fellowship-trained

surgeons were given a tutorial on the proposed classification sys-

tem. Each of the blinded observers individually reviewed the

intraoperative photographs and allocated scores to the each of the 4

zones and an overall grade to each patient. Scores were compared

between observers to assess interobserver reliability. Each of the 6

blinded observers were given the same clinical pictures and asked

to rescore bone and soft tissue injury according to the proposed

classification to determine intraobserver reliability. The use of

photographs allowed documentation and prevented exposure of

the open knee wound to multiple observers.

Classification System

The proposed classification is called the macroscopic soft tissue

injury (MASTI) score. The MASTI classification system is based on

an intraoperative assessment of the soft tissue envelope in TKA. The

classification system divides the knee into the 4 following zones:

medial tibial zone; lateral tibial zones; anterior zone (the extensor

mechanism, patella and quadriceps tendon); and posterior zone.

The tibia is divided into a medial and lateral zone by a horizontal

line from the PCL towards the most prominent point of the tibial

tubercle (Fig. 1). The posterior zone includes the PCL and posterior

capsule, which is most easily evaluated in deep knee flexion. The

zones of the knee are evaluated for iatrogenic soft tissue injury. In

our series, all cases were cruciate substituting prosthesis.

The macroscopic appearances of the soft tissue injuries in each

of the 4 zones are evaluated. There are 6 potential soft tissue

appearances, and the score designated to each zone reflects the

most severe soft tissue injury within that zone. Different point

values are assigned to the corresponding soft issue macroscopic

appearance for each zone (Fig. 2).

This includes:

6. Uninvolved soft tissue (10 points)

5. Planned soft tissue release (8 points)

4. Soft tissue contusion (7 points)

3. Soft tissue fibrillation (macroscopic incomplete damage)

(5 points)

2. Soft tissue cleavage (3 points)

1. Complete unintentional soft tissue detachment (superficial

medial collateral ligament tear, lateral collateral ligament tear,

partial or full patella tendon tear) (0 points)

Using this classification system, a maximum of 40 points may be

awarded if there is no evidence of iatrogenic soft tissue injury in

any of the 4 zones. If there is complete unintentional soft tissue

detachment in any of the 4 zones, then the patient scores 0 points

for all 4 compartments. The minimum score is therefore zero

points. The grading system for each zone has been weighted to

enable the total score of all 4 zones to accurately reflect the severity

of periarticular knee injury and enable stratification of this infor-

mation into 4 distinct groups (A-D) (Table 2).

Group A (34-40 points) indicates that the periarticular soft tis-

sue envelope is well preservedwithmild to no iatrogenic soft tissue

injury in all 4 zones. Group B (25-33 points) indicates that there is

moderate iatrogenic periarticular soft tissue injury with clear soft

tissue injury in at least 2 zones. Group C (24-1 points) indicates

more severe soft tissue injury with iatrogenic soft tissue injury to

least 3 of the 4 zones. Group D (0 points) indicates surgical trauma

or complete disruption that has resulted in defunctioning of the

superficial medial collateral ligament, lateral collateral ligament, or

the extensor mechanism (patella or quadriceps tendon) irre-

spective of the soft tissue appearance in any other corresponding

compartment.

The quality of the femoral and tibial bony surfaces is also

evaluated and used to stratify the soft tissue injury score further.

There are 3 distinct grades for the macroscopic appearance of the

cut femoral and tibial surface. Grades are assigned to the femur

(“F”) and tibia (“T”) based on the most injured part of the bone

cuts. Grade A indicates that the cut bone surfaces are pristine and

unblemished. Grade B indicates that the bony surfaces are

Table 1

Baseline Characteristics for Patients Undergoing RA-TKA and CJ-TKA.

RA-TKA (n¼30) CJ-TKA (n¼30) P Value

Age, y (range) 68.5 (43-84) 69.9 (42-86) .912

Gender (M/F) 14/16 13/17 1

BMI (kg/m2) 29.15 ± 4.5 30.68 ± 4.7 1

Side (left/right) 12/18 16/14 .272

Coronal deformity (mean ± SD) 4.80! ± 5.718! 3.04! ± 7.0! .363

Correctible coronal deformity 15/15 13/17 .77

Sagittal deformity (mean ± SD) 5.75! ± 3.9! 5.81! ± 4.3! .958

ASA grade (mode; range) 2 (1-3) 2 (1-3) 1

ASA, American Society of Anesthesiologists; BMI, body mass index; CJ-TKA, con-

ventional jig-based total knee arthroplasty; RA-TKA, robotic-arm assisted total knee

arthroplasty; SD, standard deviation.

Fig. 1. Diagrammatic representation of the macroscopic soft tissue injury (MASTI)

score showing tibial plateau in the axial plane.

B. Kayani et al. / The Journal of Arthroplasty xxx (2018) 1e6 3

uneven or were inadvertently injured or damaged when per-

forming the bone cuts. Grade C indicates that repeat bone

resection may be necessary to improve the bony surface condi-

tion and that tibial and/or femoral wedges may be necessary to

restore the joint line.

Statistical Analysis

All the datawere analyzedwith statistical IBM SPSS (IBM SPSS, V

24, Armonk, NY, IBM Corp) software package. Throughout the

process, a tool for assessing reliability (Cronbach's alpha >0.95) was

used. All the variables were described by inputting the percentages

and the number of cases as categorical variables. The quantitative

variables were described as an average and a standard deviation.

The suitability study was done by calculating the intraclass corre-

lation coefficient (ICC), also denominated the “internal correlation

coefficient” or “reliability coefficient”, with a confidence interval of

95%. The inference was studied using the chi-square test or Fisher's

exact test, as required. The inference was carried out using t test.

The level of significance was set at P < .05.

Results

MASTI Score

The overall MASTI score was greater in patients undergoing

RA-TKA compared with CJ-TKA (30.85 ± 3.1 vs 27.68 ± 3.9,

respectively, P < .05). Patients receiving RA-TKA had increased

grade A scores (10/30 vs 2/30, P < .05) and reduced grade C scores

(0/30 vs 8/30, P < .05) compared with CJ-TKA. There was no

difference in RA-TKA and CJ-TKA in grade B scores (18/30 vs 20/30,

P¼ .21) and no patients in either group received grade D scores. The

odds ratio showed RA-TKA was 5.6 times more likely to have a

grade A score than CJ-TKA.

Interobserver and Intraobserver Correlation

There was high interobserver (ICC 0.92 [95% CI: 0.88-0.96],

P < .05) and intraobserver agreement (ICC 0.94 [95% CI: 0.92- 0.97],

P < .05) between the 6 blinded observers in relation to the MASTI

classification system.

Bone Injury Score

Intraoperative assessment of femoral and tibial bone resections

followed a similar trend with reduced iatrogenic bone injury scores

in RA-TKA compared with CJ-TKA. The use of RA-TKA was associ-

atedwithmore pristine type A femoral (30/30 vs 12/30, P < .05) and

tibia (26/30 vs 15/30, P < .05) bone cuts compared with CJ-TKA.

Type B bone cuts were less common in RA-KA for both femur (0/

30 vs 18/30, P < .05) and tibia (4/30 vs 15/30, P < .05) compared to

CJ-TKA. No patients in either group had type C femoral or tibial

bone resection surfaces.

Soft Tissue Injury

In patients with both correctible and noncorrectible deformities,

RA-TKA was associated with reduced medial soft tissue release

compared to CJ-TKA (Table 3). Of note, none of the patients in the

RA-TKA group required complete release of the posterior oblique

ligament and posterior capsule compared with 10 patients in the

CJ-TKA group.

Table 2

Description of the MASTI Classification System.

MASTI

Classification

Description of Soft

Tissue Preservation

Points Description

Grade A Excellent >34 points Iatrogenic injury to only 1

zone with relative soft

tissue preservation of the

other zones

Grade B Average 25-33 points Minimal iatrogenic injury

to #2 zones with relative

soft tissue preservation of

the other zones

Grade C Poor <24 points Significant iatrogenic soft

tissue injury to #3 zones

Grade D Defunctioned knee 0 Injury to superficial MCL ±

LCL ± extensor mechanism

defunctioning the knee

LCL, lateral collateral ligament; MASTI, macroscopic soft tissue injury; MCL, medial

collateral ligament.

Fig. 2. Intraoperative photographs showing soft tissue injury for each grade of MASTI

classification system. No type 6 injuries were observed in this study. LCL, lateral

collateral ligament; MCL, medial collateral ligament.

B. Kayani et al. / The Journal of Arthroplasty xxx (2018) 1e64

Alignment and Fixed Flexion Deformity (FFD)

In the cohort of patients who underwent RA-TKA, there was no

correlation between preoperative FFD and the proposed MASTI

score (Pearson's coefficient ¼ $0.29, P ¼ .2). The extent of preop-

erative malalignment did not correlate with the proposed MASTI

score (Pearson's coefficient ¼ $0.21, P ¼ .36). The clinical correct-

ability of preoperative malalignment did not have an impact on the

soft tissue classification score (Pearson's coefficient ¼ $0.17,

P ¼ .41). In the group that underwent CJ-TKA, the extent of FFD

weakly correlated with proposed MASTI score (Pearson's

coefficient ¼ $0.35, P < .05). In this group, there was a negative

correlation between the extent of preoperative malalignment and

proposed MASTI score (Pearson's coefficient ¼ $0.73, P < .05).

Discussion

This study showed that RA-TKA was associated with reduced

bone and periarticular soft tissue injury compared with CJ-TKA. The

MASTI classification system had high interobserver and intra-

observer reliability for reporting the extent of iatrogenic bone and

soft tissue injury during TKA. This proposed classification system

may help to standardize reporting of bone and soft tissue injury

during TKA and facilitate further research correlating periarticular

soft tissue injury with different surgical techniques to long-term

clinical outcomes and implant survivorship.

Accurate bone resection, implant positioning, and ligamentous

tensioning are fundamental to achieving well-balanced flexion and

extension gaps in TKA. Suboptimal soft tissue balancingmay lead to

increased risk of implant wear, instability, aseptic loosening, and

revision surgery [3,21e25]. However, there is no uniform

consensus on the sequence or extent to which these soft tissue

releases should be performed to achieve balanced flexion and

extension gaps, with some authors suggesting that all TKAs per-

formed without navigation should undergo ligamentous releases,

whereas others suggest that soft tissue balancing may only be

appropriate in 50%-76% of cases [24e26]. In this study, intra-

operative dynamic tracking enabled the surgeon to assess on-table

alignment through the arc-of-motion, stability, range of movement,

and laxity with varus and valgus straining. None of the patients

undergoing RA-TKA required release of the posterior oblique liga-

ment or posteromedial capsule and overall RA-TKA had reduced

medial soft tissue releases compared with those undergoing CJ-

TKA, despite no difference between the 2 groups relating to pre-

operative alignment and passive correctability. In the RA-TKA

group, intraoperative manipulation and modifications to femoral

and tibial bone cuts based on live onscreen changes in alignment

and stability helped to achieve balanced flexion and extension gaps,

without the need for extensive soft tissue releases.

Bone resection in RA-TKA was performed using an oscillating

saw with visual, auditory, and tactile feedback. The sawblade in

RA-TKA was only active within the confines of the stereotactic

boundaries, which may have helped to better protect the peri-

articular soft tissue envelope compared to the manually controlled

sawblade in CJ-TKA. Our findings are in keeping with a previous

cadaveric study in which 6 blinded observers reported soft tissue

trauma in cruciate-retaining TKAs and found RA-TKA was associ-

ated with reduced PCL injury, tibial subluxation, and patella ever-

sion compared with CJ-TKA [20]. In our study, there was no gross

ligamentous disruption in either treatment group, and the soft

tissue trauma may be considered subtle subclinical findings, but

previous studies on knee arthroplasty have shown that even

limited soft tissue releases may promote changes in local and sys-

temic inflammatory responses, leading to increased pain and

delayed postoperative rehabilitation [26e29]. Siebert et al [30]

retrospectively reviewed 70 patients who underwent RA-TKA and

50 who had CJ-TKA and reported that soft tissue swelling was far

less in the former. The authors also reported that sawblade action

confined to the boundaries of the stereotactic window in the ro-

botic group may have helped to better control bone resection and

limit injury to the periarticular soft tissue envelope.

In this study, we found that the conceptual benefits of the ste-

reotactic window in RA-TKA were transferrable to clinical practice

with reduced bone and soft tissue injury compared to CJ-TKA, but

these findings should be interpreted with caution as there is no

existing evidence correlating these periarticular injuries to long-

term clinical results, functional outcomes, or long-term implant

survivorship. Furthermore, patients undergoing RA-TKA had

improved MASTI scores compared to CJ-TKA, but the clinical

significance of the difference in mean scores between the 2 treat-

ment groups is unknown at this stage. Studies have reported

improved accuracy of implant positioning and short-term func-

tional outcomes in RA-TKA compared to CJ-TKA [31e35], and the

results of further higher quality studies comparing clinical

outcomes, patient-reported outcome measures, complications,

cost-effectiveness, and implant survival between the 2 surgical

techniques are still awaited.

The MASTI classification system provides a structured and sys-

tematic approach to reporting bone and periarticular soft tissue

injury during TKA. To our knowledge, this is the only grading sys-

tem for recording periarticular injury in TKA. Despite its short-

comings in these early stages, this objective and validated

classification system assesses a comprehensive range of outcomes

from the soft tissue envelope and stratifies femoral and tibial bone

injury. The high interobserver validity of the classification will also

aid the adoption and integration of this grading system into clinical

practice. The MASTI classification systemmay be used as a guide to

analyze and record periarticular injury during TKA in more detail;

standardize data collection between treatment centers; correlate

postoperative pain, rehabilitation, and inflammatory response to

the extent of soft tissue releases; and facilitate further research

comparing the invasiveness of different surgical approaches to

long-term clinical outcomes and implant survivorship.

There are several limitations to this study which need to be

considered when interpreting the findings. First, the MASTI score

provides a general grade for bone and soft tissue injury during TKA

with limited information on the state of the individual compart-

ments of the knee joint. Second, the classification system was

constructed using cruciate-sacrificing implants and further modi-

fications may subsequently be required with cruciate-retaining

implant designs. Third, clinical photographs were used for assess-

ment and determination of the grade of soft tissue injury as

Table 3

Medial Soft Tissue Releases in Study Patients With Correctable and Noncorrectable

Coronal Deformities.

RA-TKA CJ-TKA P Value

Noncorrectable coronal deformity 15 12

Medial zone soft tissue release <.05

None 8 2

<50% 7 5

Complete 0 5

Release of POL and posteromedial capsule

Correctable coronal deformity 15 18

Medial zone soft tissue release <.05

None 3 3

<50% 12 10

Complete 0 5

Release of POL and posteromedial capsule

CJ-TKA, conventional jig-based total knee arthroplasty; RA-TKA, robotic

armeassisted total knee arthroplasty; POL, posterior oblique ligament.

B. Kayani et al. / The Journal of Arthroplasty xxx (2018) 1e6 5

opposed to determining injury at the time of the surgical proced-

ure. Fourth, the impact of this periarticular injury on the systemic

inflammatory response, which can affect postoperative pain, and

early functional recovery was not assessed in this study. Fifth, the

majority of arthroplasty surgeons currently use CJ-TKA and so any

potential benefits of this RA-TKA on bone and soft tissue injurymay

be purely academic until further studies correlating these benefits

to long-term clinical outcomes are published.

Conclusion

Patients undergoing RA-TKA had decreased bone and peri-

articular soft tissue injury compared to those undergoing CJ-TKA.

The proposed MASTI classification system had high interobserver

and intraobserver reliability for assessing bone and soft tissue

injury during TKA and may facilitate further research comparing

and correlating the invasiveness of different surgical techniques to

long-term clinical outcomes and implant survivorship.

References

[1] National Joint Registry for England andWales 9th Annual Report. http://www.njrcentre.org.uk [accessed 15.03.18].

[2] Griffin FM, Insall JN, Scuderi GR. Accuracy of soft tissue balancing in total kneearthroplasty. J Arthroplasty 2000;15:970e3.

[3] Mihalko WM, Whiteside LA, Krackow KA. Comparison of ligament-balancingtechniques during total knee arthroplasty. J Bone Joint Surg Am

2003;85(Suppl 4):132e5.

[4] Peters CL, Mohr RA, Bachus KN. Primary total knee arthroplasty in the valgusknee: creating a balanced soft tissue envelope. J Arthroplasty 2001;16:721e9.

[5] Ranawat CS, Rose HA, Rich DS. Total condylar knee arthroplasty for valgus andcombined valgus-flexion deformity of the knee. Instr Course Lect 1984;33:412e6.

[6] Whiteside LA. Soft tissue balancing: the knee. J Arthroplasty 2002;17(Suppl

1):23e7.[7] Whiteside LA, Saeki K, Mihalko WM. Functional medical ligament balancing in

total knee arthroplasty. Clin Orthop Relat Res 2000;380:45e57.[8] Peters CL, Jimenez C, Erickson J, Anderson MB, Pelt CE. Lessons learned from

selective soft-tissue release for gap balancing in primary total knee arthro-plasty: an analysis of 1216 consecutive total knee arthroplasties. J Bone Joint

Surg Am 2013;95:e152.

[9] Berger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining therotational alignment of the femoral component in total knee arthroplasty

using the epicondylar axis. Clin Orthop Relat Res 1993;286:40e7.[10] Katz MA, Beck TD, Silber JS, Seldes RM, Lotke PA. Determining femoral rota-

tional alignment in total knee arthroplasty: reliability of techniques.

J Arthroplasty 2001;16:301e5.[11] Fehring TK. Rotational malalignment of the femoral component in total knee

arthroplasty. Clin Orthop Relat Res 2000;380:72e9.[12] Dennis DA, Komistek RD, Kim RH, Sharma A. Gap balancing versus measured

resection technique for total knee arthroplasty. Clin Orthop Relat Res2010;468:102e7.

[13] Lee G-C, Lotke PA. Management of intraoperative medial collateral ligament

injury during TKA. Clin Orthop Relat Res 2011;469:64e8.[14] McNabb D, Kim R, Springer B. Instability after total knee arthroplasty. J Knee

Surg 2014;28:097e104.[15] Lynch AF, Rorabeck CH, Bourne RB. Extensor mechanism complications

following total knee arthroplasty. J Arthroplasty 1987;2:135e40.

[16] Rand JA, Morrey BF, Bryan RS. Patellar tendon rupture after total knee

arthroplasty. Clin Orthop Relat Res 1989;244:233e8.[17] Zan P, Wu Z, Yu X, Fan L, Xu T, Li G. The effect of patella eversion on

clinical outcome measures in simultaneous bilateral total knee arthro-plasty: a prospective randomized controlled trial. J Arthroplasty 2016;31:

637e40.

[18] Siqueira M, Haller K, Mulder A, Goldblum AS, Klika AK, Barsoum WK. Out-comes of medial collateral ligament injuries during total knee arthroplasty.

J Knee Surg 2014;29:068e73.[19] Bates MD, Springer BD. Extensor mechanism disruption after total knee

arthroplasty. J Am Acad Orthop Surg 2015;23:95e106.[20] Khlopas A, Chughtai M, Hampp EL, Scholl LY, Prieto M, Chang TC, et al. Ro-

botic-arm assisted total knee arthroplasty demonstrated soft tissue protec-

tion. Surg Technol Int 2017;30:441e6.[21] Chauhan SK, Clark GW, Lloyd S, Scott RG, Breidahl W, Sikorski JM. Computer-

assisted total knee replacement. A controlled cadaver study using a multi-parameter quantitative CT assessment of alignment (the perth CT protocol).

J Bone Joint Surg Br 2004;86:818e23.

[22] Elkus M, Ranawat CS, Rasquinha VJ, Babhulkar S, Rossi R, Ranawat AS. Totalknee arthroplasty for severe valgus deformity. Five to fourteen-year follow-

up. J Bone Joint Surg Am 2004;86-A:2671e6.[23] Engh GA. The difficult knee: severe varus and valgus. Clin Orthop Relat Res

2003:58e63.

[24] Nagamine R, Kondo K, Ikemura S, Shiranita A, Nakashima S, Hara T, et al.Distal femoral cut perpendicular to the mechanical axis may induce varus

instability in flexion in medial osteoarthritic knees with varus deformity intotal knee arthroplasty: a pitfall of the navigation system. J Orthop Sci

2004;9:555e9.[25] Ridgeway SR, McAuley JP, Ammeen DJ, Engh GA. The effect of alignment of the

knee on the outcome of unicompartmental knee replacement. J Bone Joint

Surg Br 2002;84:351e5.[26] Laskin RS, Beksac B, Phongjunakorn A, Pittors K, Davis J, Shim JC, et al.

Minimally invasive total knee replacement through a mini-midvastus inci-sion: an outcome study. Clin Orthop Relat Res 2004:74e81.

[27] Niki Y, Mochizuki T, Momohara S, Saito S, Toyama Y, Matsumoto H. Is mini-

mally invasive surgery in total knee arthroplasty really minimally invasivesurgery? J Arthroplasty 2009;24:499e504.

[28] Bradley B, Middleton S, Davis N, Williams M, Stocker M, Hockings M, et al.Discharge on the day of surgery following unicompartmental knee

arthroplasty within the United Kingdom NHS. Bone Joint J 2017;99-B:788e92.

[29] Cody JP, Pfefferle KJ, Ammeen DJ, Fricka KB. Is outpatient unicompartmental

knee arthroplasty safe to perform at an ambulatory surgery center? Acomparative study of early post-operative complications. J Arthroplasty

2017;33:10e6.[30] Siebert W, Mai S, Kober R, Heeckt PF. Technique and first clinical results of

robot-assisted total knee replacement. Knee 2002;9:173e80.

[31] Song EK, Seon JK, Yim JH, Netravali NA, Bargar WL. Robotic-assisted TKA re-duces postoperative alignment outliers and improves gap balance compared

to conventional TKA. Clin Orthop Relat Res 2013;471:118e26.[32] Bellemans J, Vandenneucker H, Vanlauwe J. Robot-assisted total knee

arthroplasty. Clin Orthop Relat Res 2007;464:111e6.[33] Kim SM, Park YS, Ha CW, Lim SJ, Moon YW. Robot-assisted implantation

improves the precision of component position in minimally invasive TKA.

Orthopedics 2012;35:e1334e9.[34] Moon YW, Ha CW, Do KH, Kim CY, Han JH, Na SE, et al. Comparison of robot-

assisted and conventional total knee arthroplasty: a controlled cadaver studyusing multiparameter quantitative three-dimensional CT assessment of

alignment. Comput Aided Surg 2012;17:86e95.

[35] Song EK, Seon JK, Park SJ, Jung WB, Park HW, Lee GW. Simultaneous bilateraltotal knee arthroplasty with robotic and conventional techniques: a pro-

spective, randomized study. Knee Surg Sports Traumatol Arthrosc 2011;19:1069e76.

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