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Computed Tomographic Analysis of Curved and StraightGuides for Placement of Suture Anchors for Acetabular Labral

RefixationShane J. Nho, M.D., M.S., Ryan L. Freedman, B.S., Andrew E. Federer, B.S.,

Richard C. Mather III, M.D., Alejandro A. Espinoza Orias, Ph.D., Vincent M. Wang, Ph.D.,and Geoffrey S. Van Thiel, M.D., M.B.A.

Purpose: The purpose of this study was to compare suture anchor placement in the acetabular rim between straight andcurved drill guides regarding angle and distance of the suture anchor tip from the articular cartilage during labral refix-ation. Methods: A total of 14 fresh-frozen cadaveric hips underwent arthroscopic labral incision from the 12 to 3 o’clockpositions and subsequent repair with either a curved drill guide or a straight drill guide. These hips were then compared bycomputed tomographic imaging analysis by measuring the angle of suture anchor insertion and the distance of the tip ofthe suture anchor to the articular cartilage at the 1 o’clock, 2 o’clock, and 3 o’clock positions. Results: The curved sutureanchor (CSA) guide significantly increased the insertion angle (P ¼ .009) and distance from the articular cartilage toanchor (P ¼ .003) at the 1 o’clock position on the acetabulum. The angle of insertion at the 2 and 3 o’clock positions wasgreater for the CSA guide compared with the straight suture anchor (SSA) guide but did not reach statistical significance.Conclusions: A CSA guide was shown to be significantly more effective in increasing the angle of insertion of sutureanchors and increased the distance of the suture anchor tip to the articular cartilage surface at the 1 o’clock position butnot at the 2 or 3 o’clock position. Clinical Relevance: The use of SSA guides can be difficult because of the osseousmorphologic characteristics of the acetabular rim, leading to placement of the suture anchor away from the acetabular rimand therefore resulting in a nonanatomical refixation of the acetabular labrum. The use of a curved guide, flexible drill,and flexible suture anchor inserter may provide more precise placement of suture anchors in the acetabular rim.

he treatment of femoroacetabular impingement

T(FAI) commonly involves reattachment of theacetabular labrum. One commonly used method ofreattachment is with suture anchors. When addressingosseous abnormalities on the acetabulum (pincerdeformity), the labrum is either incised from theacetabular rim, or rim trimming occurs above thelabrum without a formal detachment. Once the pincer

From Division of Sports Medicine, Department of Orthopaedic Surgery, Hipreservation Center, Rush University Medical Center, Rush Medical College,ush University, Chicago, Illinois, U.S.A.The authors report the following potential conflict of interest or source ofnding in relation to this article: S.J.N. is a paid consultant for Stryker, Pivotedical, and Ossur and receives research support from Stryker, Pivot Medical,nd Allosource.Received January 9, 2013; accepted July 9, 2013.Address correspondence to Shane J. Nho, M.D., M.S., Midwest Orthopae-

ics at Rush, 1611 West Harrison Street, Suite 300, Chicago, IL 60612, U.S.A.-mail: shane.nho@rushortho.com� 2013 by the Arthroscopy Association of North America0749-8063/1328/$36.00http://dx.doi.org/10.1016/j.arthro.2013.07.262

Arthroscopy: The Journal of Arthroscopic and Related Sur

deformity is completely removed, arthroscopic labralrefixation is performed by inserting multiple sutureanchors in the acetabular rim.1-6 Labral refixationappears to have better outcomes than debridement.1,3

Furthermore, arthroscopic surgery for FAI has beenshown to have equal or better outcomes than opensurgery.7,8

Anatomic labral refixation is technically challengingbecause of the morphologic characteristics of theacetabular rim, the angle of suture anchor insertion, andthe size of the suture anchor. At present, instrumenta-tion and implants from the shoulder have been adoptedbut have been designed to be longer to accommodatethe deeper hip joint. The angle of insertion for sutureanchors is important because an anatomical acetabularlabral repair requires the anchors to be placed as closeto the articular cartilage surface as possible, but it hasthe potential to cause iatrogenic cartilage injury causedby the trajectory of anchor insertion. The use of a curveddrill guide, flexible drill, and flexible suture anchorinserter may provide more accurate placement of sutureanchors around the acetabular rim. The aim of our

gery, Vol 29, No 10 (October), 2013: pp 1623-1627 1623

Fig 1. Suture drill guides. (A) Straight drill guide (0�). (B)Curved drill guide (25�).

Fig 2. Fixation and portal placement of cadaveric hip spec-imen. Three-portal technique was used with an anterolateralportal (a), anterior portal (b), and distal anterolateral acces-sory portal (*). (A, anterior; D, distal; L, lateral; M, medial; P,posterior; Pr, proximal.)

1624 S. J. NHO ET AL.

present study was to compare suture anchor insertionusing either a straight or curved drill guide in a cadavericmodel. Our hypothesis was that the curved drill guidewould allow placement of suture anchors with a greatersafety margin without the anchors penetrating theacetabular articular cartilage surface.

Methods

Study DesignNine human fresh-frozen cadaveric pelvises from

Anatomical Service (Schiller Park, IL) and the Anatom-ical Gift Association of Illinois (Chicago, IL) were halvedand harvested. There were 2 male and 7 female donorsaveraging 77.9 years (SD� 10.91; range, 59 to 89 years).Computed tomographic scans were obtained for eachhemipelvis before surgical intervention. Of the 18 hipsavailable to undergo arthroscopic surgery, 4 wereexcluded because of Tönnis grade greater than 2 asdetermined by computed tomographic scan; therefore,there were 14 hips available for the study. The firstspecimen of each group of paired hips was blindly

selected and alternately assigned to one of the sutureanchor drill guides by a single board-certified fellowship-trained orthopaedic surgeon (R.C.M.), and the contra-lateral sidewas treatedwith the other drill guide: straightsuture anchor (SSA) guide insertion (TwinLoop FLEX0� guide; Stryker, Mahwah, NJ) or curved suture anchor(CSA) guide insertion (TwinLoop Flex 25� guide;Stryker) (Fig 1).

Surgical TechniqueThe specimenwas placed in a hip traction jig (Stryker),

with the iliac crest and femur fixed to the device (Fig 2),and traction was applied to obtain 1 cm of joint distrac-tion. The surgical technique was the same for bothgroups, except for the drill guide used for suture anchorinsertion. An anterior portal was placed at the intersec-tion between the vertical line drawn from the anteriorsuperior iliac spine and the horizontal line drawn fromthe tip of the greater trochanter. Standard anterolateraland anterior portals were established, and an interportalcapsulotomy was created to connect the anterolateralportal and the anterior portal. Soft tissue of the acetab-ulum was ablated to expose the acetabular labrum, anda 5.5-mmarthroscopic spherical burwas used to trim theacetabular rim in the anterosuperior quadrant. Thelabrum was detached from the 12 to 3 o’clock position(right hip) with a disposable arthroscopic blade. Speci-mens were treated according to their random assign-ment. Three single-loaded suture anchors (3.5-mm

Fig 3. Computed tomographic measurements. (A) Lateral center edge angle. (B) Angle of insertion of anchor at 1 o’clockposition. (C) Distance from tip of anchor to articular cartilage for the anchor at 1 o’clock position.

CT ANALYSIS CURVED VERSUS STRAIGHT SUTURE ANCHORS 1625

PEEK TwinLoop anchor; Stryker) were drilled andplaced at the 1, 2, and 3 o’clock positions around theacetabulum through the distal accessory anterolateralportal with either the curved or straight drill guide.During anchor placement, the curved drill was orientedin a path divergent from the acetabular cartilage. For all3 suture anchors, a mattress stitch was placed throughthe labrum using a tissue-penetrating device and wastied with reverse half hitches and alternating posts.Computed tomographic scanning was able to confirmappropriate placement of the anchor according to theclock face description, and there was no significantvariance between CSA and SSA placement in respect tothe clock face.

Computed Tomographic AnalysisThe postoperative computed tomographic images

of each cadaveric hip that underwent arthroscopiclabral repair were analyzed with 1-mm axial slices.Coronal and sagittal reconstructions were created. Twoorthopaedic surgeons (G.S.V.T. and S.J.N.) who wereblinded to the treatment groups measured the radio-graphic parameters using PACS digital tools. The inter-observer reliability showed a high level of agreement(0.94) based on separate measurements of lateral centeredge angle (LCEA) and the calculated correlation. Thevalues for LCEA were measured on the coronal images.The insertion angle was measured by extending a line 2cm from the insertion point to the acetabular cartilage asdescribed by Lertwanich et al.4 and then a second linethrough the anchor. The distance from the tip of theanchor was then measured to the closest point on theacetabular articular surface (Fig 3). On the coronalimages, the angle of anchor insertion was measured atthe 1 and 2 o’clock anchors, and the distance from the tipof the anchor to the articular cartilage for the 1 and 2o’clock anchors was also measured. The anchor at the 3o’clock position had the same measurements taken onthe axial computed tomographic scan.

Statistical AnalysisStatistical analysis was conducted using SPSS software

V.19 (SPSS, Chicago, IL). For computed tomographicanalysis, t tests were used to compare between SSA andCSA for LCEA; alpha angle; angle of insertion at the 1,2, and 3 o’clock positions; and the distance from tip tocartilage at the 1, 2, and 3 o’clock positions. P less than.05 was considered statistically significant.

ResultsComputed tomographic analysis was completed for

the 14 cadaveric hip specimens. The mean LCEA anglewas 44.74� (SD � 8.29; range, 29.0� to 59.3�), but therewas no statistically significant difference between theCSA and SSA groups. The mean alpha angle for thespecimens was 44.99� (SD � 16.33; range, 36.3� to99.7�) on coronal images. The mean 1 o’clockepositionangle of insertion was found to be significantly differentbetween the CSA (58.6�) and the SSA (35.8�) speci-mens (P ¼ .009). Additionally, the distance to articularcartilage at the 1 o’clock position was found to besignificantly different between the CSA (12.7 mm) andthe SSA (9.5 mm) specimens (P ¼ .03). There was nota statistically significant increase of the angle of inser-tion at the 2 o’clock position (Table 1). There was nopenetration of articular cartilage seen during computedtomographic analysis or gross inspection.

DiscussionLabral refixation after acetabular rim trimming is

challenging, and nonanatomical suture anchor place-ment can compromise labral function or cause iatro-genic injury to the articular cartilage.1-3 The currentstudy showed that CSA provides a greater angle ofinsertion and distance from the anchor tip to cartilage atthe 1 o’clock position and is therefore less likely tocause iatrogenic cartilage injury because of an improvedtrajectory. There was also a greater insertion angle andtip to cartilage distance at the 2 and 3 o’clock positions

Table 1. Computed Tomographic Analysis of Curved Suture Anchor (CSA) Versus Straight Suture Anchor (SSA)

Variable

CSA SSA

P ValueMean SD Range Mean SD Range

LCEA 42.8� 10.5� 29.0�-59.3� 46.7� 4.5� 40.0�-53.3� .151 o’clock position (angle) 58.6� 14.5� 37.8�-78.7� 35.8� 5.8� 30.8�-47.1� .009*Distance to cartilage (mm) 12.7 2.4 10.9-16.4 9.5 1.5 7.9-11.8 .03*2 o’clock position (angle) 65.1� 12.9� 45.4�-77.4� 49.4� 11.0� 35.2�-66.0� .09Distance to cartilage (mm) 14.0 3.4 10.4-19.2 11.6 1.6 9.1-13.4 .23 o’clock position (angle) 26.7� 5.4� 20.7�-34.7� 20.2� 13.6� 9.0�-46.1� .17Distance to cartilage (mm) 8.3 2.5 4.4-11.2 6.4 3.7 4.0-13.8 .24

CSA, curved suture anchor; LCEA, lateral center edge angle; SD, standard deviation; SSA, straight suture anchor.*Denotes statistical significance.

1626 S. J. NHO ET AL.

for the CSA compared with the SSA, but it did not reachstatistical significance.The goal of an anatomical labral refixation is to place

the suture anchor as close to the articular cartilagesurface as possible without penetrating the cartilage.6,9

The consequences of suture anchors placed too farfrom the articular cartilage surface can lead to eversionof the labrum, therefore compromising the suction sealand stabilizing role and increasing contact pressure.9

Placement of the drill too close to the articular carti-lage surface can cause iatrogenic cartilage injury.The osteologic features of the acetabulum contribute

to the difficulty of proper anchor insertion. “Dangerangles” as part of surgical methods to avoid jointpenetration have been documented.4 As the anchorsare placed more anterior at the 3 o’clock position, theacetabular rim becomes more narrow, and anchorinsertion is more likely to cause injury to the cartilagesurface, unicortical drilling, and anchor placement inthe surrounding ilipsoas muscle belly.4 Anteroposteriorfluoroscopic imaging can be used to confirm a safetrajectory that is divergent from rim cartilage foranchors placed at the 12 o’clock position.With rim trimming, as seen in the pincer component

of FAI, the margin for error (ie, safety angle) increases,as it does with smaller diameter, shorter or suture-based suture anchors, and greater radius of curvatureof the CSA. A more posterior location of the distalaccessory portal (DAP) may give a better trajectory thana modified midanterior portal or midanterior portal, butthe femoral head may impede optimal placement mostwith DAP, followed by the modified midanterior portal,and least with the midanterior portal. A more posteriorlocation of the DAP could have achieved safety marginssimilar to those of the CSA, but the goal of the studywas to determine whether a curved drill guide is moreeffective (ie, anchor placement closer to the articularcartilage) and safer (ie, lower likelihood of cartilagepenetration) compared with a standard straight anchorregardless of portal or anchor size.Computed tomographic analysis showed that the CSA

was better than the SSA guide at increasing the angle of

insertion at the 1 o’clock position, as well as increasingthe distance between the anchor tip to cartilage in the 1o’clock position. The CSA guide resulted in a greaterangle of insertion at the 2 o’clock position, but it wasnot statistically significant. The 3 o’clock position hadthe smallest insertion angle. With the small margin oferror at the 3 o’clock position, the CSA showeda greater distance to the cartilage surface, but it was notstatistically significant. The findings are relevant forboth labral repair and reconstruction. Applicability toposterior wall refixation may entail posterior-wardorientation, which was not evaluated in this study.Future studies will have to evaluate the trajectory ofanchor placement around the entire circumference ofthe acetabulum.There are several advantages of the CSA. The risk of

iatrogenic cartilage injury is common and likely un-derreported. The goal of suture anchor placement in thehip is to place the anchor as close to the articularcartilage as possible without causing cartilage penetra-tion or delamination. With the SSA, the trajectory ofthe drill and anchor will aim in the direction of the drillguide. With the CSA, the trajectory of the drill andanchor will be directed away from the undersurface ofthe cartilage. The findings of the present study confirmthat the distance between the suture anchor tip andarticular cartilage at the 1 o’clock position is greater inthe CSA group. In addition, the hip can be difficult toaccess and may require multiple percutaneous portalsfor anchor placement. The CSA system allows thesurgeon to work through a single portal to achieveanchor placement to the medial and lateral extent ofthe anterosuperior quadrant of the acetabulum rim.The present study was a controlled laboratory cada-

veric study comparing 2 different drill guides for sutureanchor placement. Each specimen was randomlyassigned to one of the suture anchor drill guides and thecontralateral side was treated with the other drill guideto increase the likelihood that the acetabular morpho-logic features were relatively similar. The orthopaedicsurgeons who measured the radiographic parameterswere blinded to the treatment groups.

CT ANALYSIS CURVED VERSUS STRAIGHT SUTURE ANCHORS 1627

LimitationsThe postprocedural computed tomographic scans had

some limitations. It was difficult to visualize the definitetip of the suture anchors because anchors are 3.5 mmlong, whereas image slices are 1 mm. The acetabularrim was hard to visualize when the image slice passedthrough the anchor at an oblique angle. These limita-tions made computed tomographic analysis of 2 hipsnot feasible. Increasing the number of reviewers of thecomputed tomographic scans as well as the number ofspecimens could have increased the reliability of theresults. Also, location of the anchors in relation tonerves was not assessed, which could factor into thesafety margin. Because the hips were randomlyassigned to each group, it was difficult to control forpoor tissue and bone quality between the 2 groups. Ifrim trimming had occurred before suture anchorplacement, a more uniform CEA angle could have beenachieved, decreasing the specimen variability.

ConclusionsThe curved suture anchor guide was shown to result

in significant increases in the anchor angle of insertionand distance from the anchor tip to the cartilage surfaceat the 1 o’clock position. The 2 and 3 o’clock positionswith the CSA showed a larger anchor tipeto-cartilagedistance, but it did not reach statistical significance.Although there were no suture anchors that penetratedthe articular cartilage surface, the CSA does provide animproved trajectory for anchor placement.

References1. Espinosa N, Rothenfluh DA, Beck M, Ganz R, Leunig M.

Treatment of femoro-acetabular impingement: Preliminaryresults of labral refixation. J Bone Joint Surg Am 2006;88:925-935.

2. Larson CM, Giveans MR. Arthroscopic debridement versusrefixation of the acetabular labrum associated with femo-roacetabular impingement. Arthroscopy 2009;25:369-376.

3. Larson CM, Giveans MR, Stone RM. Arthroscopicdebridement versus refixation of the acetabular labrumassociated with femoroacetabular impingement: Mean 3.5-year follow-up. Am J Sports Med 2012;40:1015-1021.

4. Lertwanich P, Ejnisman L, Torry MR, Giphart JE,Philippon MJ. Defining a safety margin for labral sutureanchor insertion using the acetabular rim angle. Am J SportsMed 2011;39:111S-116S (suppl).

5. Philippon MJ, Arnoczky SP, Torrie A. Arthroscopic repairof the acetabular labrum: A histologic assessment of heal-ing in an ovine model. Arthroscopy 2007;23:376-380.

6. Philippon MJ, Schroder E, Souza BG, Briggs KK. Labrum:Resection, repair and reconstruction sports medicine andarthroscopy review. Sports Med Arthrosc 2010;18:76-82.

7. Matsuda DK, Carlisle JC, Arthurs SC, Wierks CH,Philippon MJ. Comparative systematic review of the opendislocation, mini-open, and arthroscopic surgeries for fem-oroacetabular impingement. Arthroscopy 2011;27:252-269.

8. Botser IB, Smith TW Jr, Nasser R, Domb BG. Open surgicaldislocation versus arthroscopy for femoroacetabular im-pingement: A comparison of clinical outcomes. Arthroscopy2011;27:270-278.

9. Safran MR. The acetabular labrum: Anatomic and func-tional characteristics and rationale for surgical intervention.J Am Acad Orthop Surg 2010;18:338-345.