esquina posteromedial rodilla

337

The anatomy of the medial side of the knee has been welldescribed.1,9,28 Anatomically, the medial supporting struc-tures can be divided into layers28 or regions.9 Functionally,the division between static (capsular and noncapsular lig-aments) and dynamic (musculotendinous units and theiraponeuroses) stabilizers must be made. The contributionsof the dynamic stabilizers of the knee and the effects ofcoupled motion on resultant injury patterns are often over-looked because they are impossible to assess with ligamentsectioning studies, which dominate the available biome-chanical literature on the topic. Nonetheless, as surely aswe understand the dynamizing effect of the vastus medi-alis obliques on patellar tracking, we must also be aware ofthe dynamic role of the semimembranosus, which is to pro-

vide motor function to the posteromedial meniscocapsularcomplex.

The work of Warren and Marshall28 focused on the con-cept of layers with little emphasis on the supporting struc-tures posterior to the “superficial medial ligament.” Giventhe lack of emphasis on the posteromedial aspect of theknee, other related functional studies have emphasized therole of the “superficial medial ligament.”26,27 As a result,when the topic of medial-sided knee injury arises, the ref-erence has become synonymous with injury to the superfi-cial medial collateral ligament.

The description of the posterior oblique ligament (POL)by Hughston and Eilers as “a discrete anatomical thicken-ing of the capsular ligament”9 and later reports assigningboth static and dynamic function to the posterior medialknee structures5,8 introduced the concept of the postero-medial corner. This concept was echoed by Müller who stat-ed, “One thing is certain: despite its close topographic rela-tion to the medial collateral ligament, the posteromedialcorner is fundamentally different in nature and functionfrom the tibial collateral ligament itself.”20

The Posteromedial Corner of the KneeMedial-Sided Injury Patterns Revisited

William F. Sims* and Kurt E. Jacobson*†‡

From the *Hughston Clinic, Columbus, Georgia, and the ‡Department of Orthopaedics, TulaneUniversity School of Medicine, New Orleans, Louisiana

Background: Medial-sided knee injury patterns have been poorly defined in the available literature. The lack of definition canbe attributed to the differing anatomic perspectives of physician authors and the functional significance they assigned to theposteromedial structures of the knee.

Hypothesis: Many so-called medial collateral ligament injuries can involve significant damage to the posteromedial corner struc-tures that may not be appreciated.

Study Design: Retrospective cohort study.

Method: The authors reviewed the charts of 93 patients (93 knees) with operatively treated isolated and combined medial-sidedknee injuries and described the associated medial injury patterns.

Results: Ninety-nine percent of the knees were found to have an injury of the posterior oblique ligament. In the series, 70% ofthe knees also had an injury of the semimembranosus capsular attachment, and 30% were found to have complete peripheraldetachment of the meniscus. Injury to the posterior oblique ligament was the common injury, but other sites of disruption capa-ble of disabling this dynamic meniscocapsular complex were present.

Conclusions: Before assigning function to the various posteromedial structures of the knee, we must better define medial-sidedinjury patterns, the purpose of the current work. From this review of medial-sided injuries in this series of patients, the authorshave come to realize that a subgroup of these knee injuries involves injuries to the posteromedial structures that are under-appreciated.

Keywords: posterior oblique ligament; posteromedial knee injury; medial knee injury; medial collateral ligament

10.1177/0363546503261738

†Address correspondence to Kurt E. Jacobson, the Hughston Clinic,6262 Veterans Parkway, Columbus, GA 31909.

The American Journal of Sports Medicine, Vol. 32, No. 2DOI: 10.1177/0363546503261738© 2004 American Orthopaedic Society for Sports Medicine

338 Sims and Jacobson The American Journal of Sports Medicine

Anatomic structures that contribute to the function ofthe posteromedial corner of the knee are the posterior hornof the medial meniscus, the POL, the semimembranosusexpansions, the meniscotibial ligaments, and the obliquepopliteal ligament. This dynamic meniscocapsular com-plex, working in a coordinated fashion, is believed to func-tion throughout the normal range of coupled motion inboth a static and dynamic fashion as a restraint to antero-medial rotatory instability (AMRI).

Anatomy and Function

The anatomy of the medial aspect of the knee extends fromthe medial edge of the patella to the medial border of theposterior cruciate ligament. The medial-sided structurescan be divided roughly into thirds (Figure 1). The medialmeniscus is intimately attached to the capsule via themeniscotibial and meniscofemoral contributions of thedeep capsule and ligamentous structures within the vari-ous regions. The structures of the anteromedial thirdinclude the loose, thin capsular ligaments covered superfi-cially by the extensor retinaculum of the quadricepsmechanism. The mid-medial structures are the deep medi-al capsular ligament and the superficial medial collateralligament. Both ligaments originate from the medialfemoral epicondyle. The deep medial capsular ligamentinserts just below the tibial articular margin and may beconceptually divided into meniscotibial (coronary) andmeniscofemoral complements. The more superficial tibialcollateral ligament has a broad, elongated insertion on theproximal medial tibia. The more superficial tibial collater-al ligament reinforces the deep ligament and is separatedby a bursa (Figure 2). Brantigan and Voshell1 described 2portions of the tibial collateral ligament, an anterior par-allel arrangement of fibers and a more posterior obliqueportion of this ligament. It is this more oblique group offibers that Hughston and Eilers9 described as the POL (lig-amentum popliteum obliquum). This anatomically sepa-rate structure originates from the adductor tubercle, pos-terior to the medial epicondyle. Distally, the ligament fansout, having 3 separate arms or expansions: (1) the tibialarm, inserting close to the margin of the articular surface;

(2) the capsular arm, continuous with the posterior cap-sule, blending with the oblique popliteal ligament; and (3)the superficial arm associated with the semimembranosustendon (Figure 3). This structure, which was described byMeyer19 in 1853 as the “posterior medial collateral liga-ment,” is intimately attached to the medial meniscus.Nonetheless, approximately two thirds of its fibers passuninterrupted from the femur to the tibia.20 Unlike the tib-ial collateral ligament, the POL is not separated from themeniscus by a bursa but has firm meniscal attachmentsand “blends intimately with the capsule of the knee jointposteriorly.”20 As stated earlier, the POL and tibial collat-eral ligament do not share the same origin.

The posteromedial one third of the knee extends fromthe posterior edge of the tibial collateral ligament to themedial edge of the posterior cruciate ligament. The majorcomponents are the POL, the semimembranosus expan-sions, the oblique popliteal ligament, and the postero-medial horn of the meniscus. Müller20 described theposteromedial corner as the “semimembranosus corner”because of the functional significance of the contribution ofthe semimembranosus muscle. Five expansions have beendescribed: (1) the pars reflexa, passing anteriorly beneaththe tibial collateral ligament and inserting directly on thetibia; (2) the direct posteromedial tibial insertion; (3) theoblique popliteal ligament insertion; (4) the expansion to

Figure 1. Anterior, middle, and posterior capsuloligamentousdivisions.

Figure 2. The relationships between the tibial collateral liga-ment, deep medial ligament, and meniscus. Note the spacebetween the tibial collateral ligament and deep medial cap-sular ligament that houses a bursa.

Vol. 32, No. 2, 2004 The Posteromedial Corner of the Knee 339

the POL; and (5) the popliteus aponeurosis expansion(Figure 4).20

Although static sectioning studies do not address thefunction of the dynamic stabilizers of the knee, it has beentheorized that by its attachment to the POL and the tibia,the semimembranosus contributes to the dynamic stabi-lization of the posteromedial corner and allows for posteri-or meniscal retraction during knee flexion.6,20,22 Thisdynamizing effect tightens the posteromedial structures ata time when they would normally be lax and at the sametime helps to prevent posteromedial meniscal impinge-ment during knee flexion (Figures 5 and 6).

Based on work by Levy et al,16 Paulos et al22 echoedMüller’s description of the “brake stop” function of the pos-teromedial meniscal horn and emphasized its function as asecondary restraint to anterior tibial translation in theACL-deficient knee.

The intimate relationships that exist between the pos-teromedial meniscus, the POL, and the semimembranosusexpansion are critical for dynamic stability of the medialside of the knee. Injury at any level of this intricate cas-cade can result in loss of this coordinated balance.Hughston et al7 described the resultant functional insta-bility as follows: “Anteromedial rotatory instability (AMRI)is an abnormal excess opening of the medial joint space inabduction at 30º of knee flexion, with a simultaneousanteromedial rotatory subluxation of the medial tibialcondyle on the central axis of the intact posterior cruciate

ligament.” Although subtle, this additional rotatory insta-bility must be distinguished from isolated open-book insta-bility in response to abduction stress testing of the flexedknee. The coupling of this AMRI component with abductionstress has been suggested by Haimes et al4 as being possi-bly “responsible for the functional instability seen in somepatients who present with what appears to be minimaljoint looseness.” In their study, the “superficial medial col-lateral ligament” is credited as the primary restraint toexternal rotation of the tibia; nonetheless, we do not seethe effect of a combined ACL posteromedial corner injuryas many patients in our study demonstrated. ACL injurycan accentuate this instability pattern; yet instrumentedlaxity testing falls short in detecting the rotatory compo-nent of this injury.

Although MRI evaluation of the posteromedial and pos-terolateral corner structures continues to improve, a care-ful physical examination continues to remain the mostreliable diagnostic tool. In addition to the subjective find-ings of medial and posteromedial knee pain and tender-ness in patients with acute injuries, consistent objectivephysical examination findings are increased laxity toabduction stress testing in 30º of knee flexion with coupledanterior rotatory subluxation of the medial tibial plateau

Figure 3. The posterior oblique ligament (POL). Note themore posterior origin, expansile insertions, and relationshipwith the posteromedial capsule and semimembranosusexpansions. Figure 4. The semimembranosus expansions. The 5 inser-

tions: (1) pars reflexa, (2) direct posteromedial tibial insertion,(3) oblique popliteal ligament insertion, (4) expansion to pos-terior oblique ligament (POL), and (5) popliteus aponeurosisexpansion. Note the investment into the POL.


on the medial femoral condyle. This finding is aided byholding the limb by the plantar surface of the foot insteadof the distal portion of the leg during abduction to allow forappreciation of the rotatory component. The examiner canappreciate anteromedial rotation of the tibial plateau onthe medial femoral condyle with slight rotatory stress inthis position. Another useful finding is the anterior drawer

test performed in external rotation7,24 while the examinerspecifically looks for anterior subluxation of the medial tib-ial plateau with the medial femoral condyle as a referenceand observes a relatively normal relationship between thelateral aspect of the tibia and femoral articulations.Finally, in conjunction with these positive tests, focal ten-derness along the posteromedial aspect of the joint line inthe area of the meniscotibial ligament, medial meniscalinstability with abduction stress testing (lateral subluxa-tion of the meniscus), and adduction stress testing (medialsubluxation of the meniscus) may be present if the menis-cotibial ligament is injured (Figure 7).13 In an attempt tofurther describe injury patterns to the medial side of theknee, we report the incidence and anatomic location ofinjuries in this surgically treated patient population withAMRI.

MATERIALS AND METHOD

We reviewed a consecutive 6-year operative experience ofthe senior author. A database search was conducted formedial-sided knee injuries from the years 1987 through1992. There were 93 operatively treated medial-sidedinjuries in 93 patients, which was approximately 15% of allmedial-sided knee injuries treated during this time period.Indications for operative treatment were either clinical orfunctional AMRI. Knee injuries that were treated acutelywere those in patients who had clinical findings of medialand posteromedial knee pain and subjective sensations ofvalgus instability combined with objective findings of sig-nificant abduction laxity and associated AMRI as definedby Hughston.6 Symptomatic, functional AMRI was an indi-cation for the operative treatment of medial knee injurieswith a greater than 6-week interval from the time ofinjury. Both isolated and combined (ie, injury involvingadditional ligamentous structures apart from the anatom-ic structures of the medial side of the knee) ligament

Figure 5. Bird’s-eye view of the proposed dynamizing actionof the semimembranosus. The large arrow represents ten-sion created in the posterior meniscocapsular complex bythe semimembranosus. Note the ability of the semimembra-nosus to tension the posterior oblique ligament (POL) and aidin posterior meniscal retraction, represented by the smallarrow.

Figure 6. Intracapsular orientation of the posteromedial cor-ner structures showing the proposed dynamizing action(arrow) of the semimembranosus. Note the relationship of thesemimembranosus capsular expansion, the posterioroblique ligament, and the posteromedial meniscus.

Figure 7. Disruption of the meniscotibial ligament. Abductionstress (left) results in lateral translation of the medial menis-cus, whereas adduction stress (right) pushes the medialmeniscus medially.


injuries were included in our sample. We reviewed theoperative notes and the associated operative injury dia-grams completed at the time of the surgical procedure. Insome patients, intraoperative photographs were also avail-able for review. We also reviewed each patient’s chart forthe results of the examination under anesthesia and thearthroscopic examination findings. An independent partycreated a data sheet containing the description of injurypatterns for each patient. The senior author confirmed thefindings by reviewing the operative summaries. Arthro-scopic examination findings were reviewed in an attemptto identify intracapsular findings that were indicative ofmore extensive posteromedial corner injury.

There were 67 men and 26 women in our series. Fifty-four percent (50/93) of their injuries were treated opera-tively within 6 weeks of the time of injury. At the time ofsurgery, the average patient’s age was 26 years old. Themost common mechanism of injury had been a sportinginjury (72%). Approximately 13% resulted from a fall andan additional 13% from motor vehicle accident–relatedinjuries. Further breakdown of the sporting injuriesrevealed that most patients had been injured while partic-ipating in football (27%), basketball (14%), or skiing (9%).Table 1 shows the number of injuries to the variousanatomic structures.

RESULTS

We found that combined injuries had occurred in 82 of the93 knees (88%). Associated ACL injuries were found in 73knees and associated posterior cruciate ligament injuriesin 2 knees. Of the 93 knee injuries reviewed, 92 knees had

TABLE 1Injured Structures in 93 Knees

Injuries

Anatomic Structure Number Percentage

Posterior oblique ligament 92 99Tibial collateral ligament 31 33Deep medial ligament 23 25Semimembranosus tendinous expansions 65 70Meniscotibial ligament and menisco-

femoral ligament 77 83Meniscus 40 43

TABLE 2Posterior Oblique Ligament Injuries in 93 Knees

Injuries


Focal

Femoral attachment 29 32Interstitial 11 12Tibial attachment 25 27

Multifocal

Femoral and tibial attachments 14 15Femoral attachment and interstitial 9 10Tibial attachment and interstitial 4 4

Total 92 99

TABLE 3Tibial Collateral Ligament Injuries in 93 Knees

Injuries


Focal


Multifocal

Femoral and tibial attachment 2 2Femoral attachment and interstitial 2 2Tibial attachment and interstitial 2 2

Total 31 33

TABLE 4Deep Medial Capsular Ligament Injuries in 93 Knees

Injuries


Focal


Multifocal

Femoral and tibial attachment 2 2Femoral attachment and interstitial 0 0Tibial attachment and interstitial 0 0

Total 23 25

TABLE 5Meniscotibial and Meniscofemoral

Ligament Injuries in 93 Knees

Injuries

Injured Structure Number Percentage

Focal

Meniscotibial ligament 44 47Meniscofemoral ligament 5 5

Combined

Meniscotibial and meniscofemoral ligaments 28 30

Total 77 83


a documented injury to the POL; 65 were focal injuries (ie,a single point of injury to the named structure), and 27were multifocal injuries (ie, multiple points of injury to thenamed structure) (Table 2). The tibial collateral ligamentwas injured in 31 of 93 knees; 25 of these disruptions werefocal injuries (Table 3). The deep medial capsular ligamentwas injured in 23 knees, and focal injuries were more com-mon than multifocal injuries (Table 4). Injury to themeniscotibial and meniscofemoral ligaments was alsorecorded (Table 5). To qualify as an injury, the disruptionhad to involve greater than one third of the medial com-partment with extension of the injury posterior to the deepmedial capsular ligament. In the case of combined injury,the operative note reported “complete peripheral detach-ment of the meniscus.” Disruption of the semimembra-nosus tendon had occurred in 65 (70%) patients, and mostcommonly involved the capsular arm (64/65). Meniscalinjuries had been recorded in 40 knees—20 peripheraltears, 17 body tears, and 3 tears that involved both thebody and periphery.

Although almost all of the knees in our study had injuryto the POL, not all had injury to the semimembranosus,and fewer yet exhibited peripheral meniscal detachment.It is clear that injury to the POL ligament is the commoninjury, but other sites of disruption, also capable of dis-abling this dynamic meniscocapsular complex, may bepresent.

From a functional standpoint, 3 basic injury patternswere discovered, with injury to the POL being common to

them all: (1) POL injury and associated injury to the cap-sular arm of the semimembranosus (70%), (2) POL injuryand complete peripheral meniscal detachment (30%), and(3) POL injury and disruption of the semimembranosusand peripheral meniscal detachment (19%) (Figure 8).(The percentages of these 3 injury patterns were not addi-tive. Rather, the third pattern is one in which the first 2injury patterns occurred together.)

DISCUSSION

When the topic of medial-sided knee injury arises, mostphysicians choose to progress to the next topic at handbecause they have already made up their minds regardingthe optimal treatment. Although it is agreed that the iso-lated tibial collateral ligament injury can do quite wellwith a period of activity modification and protective brac-ing, more extensive injury that involves the meniscus andposteromedial corner may deserve further consideration ofoperative treatment.

Although not currently a widely held concept, we believethere is a subset of patients with medial-sided injuries inwhom the injury requires surgical repair. The patient weare referring to is one with either an isolated medial injuryor a medial injury with an associated ACL injury whodemonstrates AMRI.7 In the case of a patient with AMRIwith ACL insufficiency, it is certainly possible to stabilizeanterior translation of the knee initially, but the long-termviability of the ACL graft and the long-term function of the

Figure 8. A, Three major injury patterns (injury to the posterior oblique ligament [POL] is common to all): (1) injury to the POL withsemimembranosus disruption, (2) injury to the POL with complete peripheral meniscocapsular detachment, and (3) POL injurywith semimembranosus injury and peripheral meniscocapsular detachment. Disruption at any level is capable of disabling thedynamizing function of the semimembranosus. B, Lateral view shows injury to the semimembranosus and POL. PMD, peripher-al meniscal detachment.


knee—in particular that of the medial meniscus—may becompromised. In the past, emphasis has been placed on abrake stop–type function of the posteromedial portion ofthe medial meniscus to straight anterior tibial translationin the ACL-deficient knee. On multiple occasions, we havebeen able to appreciate the absence of the rotatory con-straint function normally seen in patients with intactmeniscotibial ligamentous attachments in patients inwhom it is deficient. The contour of the superior medialedge of the meniscus engages the medial femoral condyleduring weightbearing; this fit combined with intact menis-cotibial attachments stabilizes the knee to anteromedialmotion of the tibia. If, however, the meniscus is not stableon its tibial platform, the meniscus and femoral condylemove as a unit, sliding over the articular surface of thetibia with no stabilizing function. The meniscotibial liga-ment insufficiency may contribute to increased stress onother structures that resist anterior and anteromedial sub-luxation and can place the articular surface of the tibiaand the meniscus itself at risk of further injury.

The purpose of our study was to prove this injury existsby describing the medial and posteromedial patterns ofknee injury. In our review of the current literature,10,11,23

we found references to a medial-sided knee injury as a dis-ruption of the medial collateral ligament. In reality, theseinjuries can be far more complex (Figures 9-11). The termmedial collateral ligament has been used to refer to boththe deep medial capsular ligament and the tibial collater-al ligament. We have purposefully avoided the term as we

Figure 9. MRI of a medial-sided knee injury reveals extensivestripping (arrow) of the medial capsular structures from theproximal tibia.

Figure 10. MRI of extensive medial-sided injury with com-plete peripheral meniscal detachment (arrow), disruption ofmeniscotibial and meniscofemoral ligaments, deep medialone-third capsular ligament, and tibial collateral ligament.Note orientation of medial meniscus.

Figure 11. MRI of extensive medial-sided injury. Note lack ofmeniscal attachment and interstitial stretch of the tibial col-lateral ligament.


documented and described injury to these structures and,more important, to the posteromedial corner structures.Whether one chooses to recognize the POL9,19,20 as a sepa-rate structure or as a thickening of the posteromedial cap-sule is a matter of semantics. On the other hand, failing toconsider the possibility of the functional contribution thatthe posteromedial corner structures lend to dynamic kneestability has more serious consequences. We believe thatwith regard to stability, the posteromedial corner, althoughit is less complex anatomically, is no less important func-tionally than the posterolateral corner.

These patterns of injury are thought to be significantbecause in this cascade-type system, in which each struc-ture is dependent on the structure(s) to which it isattached or its attachment, damage at any level is capableof disabling the functional cascade of the posteromedialcapsule. The significance of understanding the varioussites of injury is that in this dynamic system, reparativePOL procedures alone may not reconstitute the menisco-capsuloligamentous complex, leaving the semimembra-nosus unable to act as the stabilizing muscle of the pos-teromedial corner.

Our review of the arthroscopic examination findings inthis consecutive series of patients revealed two intra-articular findings that although not statistically signifi-cant, we believe are indicative of more extensive postero-medial corner injury. Only 31 of the 93 patients had had aconcurrent arthroscopic examination. However, 19 of these31 patients had either gross elevation of the meniscus offthe tibia during abduction stress testing with the knee in30º of flexion, which we have called “meniscal rise” (Figure12), or posteromedial capsular hemorrhage evident duringarthroscopy.

There are several pertinent topics related to injuries ofthe posteromedial corner that should be discussed further:

(1) Why do some ACL injuries do quite well when treatednonoperatively? (2) After ACL reconstruction, why doesKT-1000 arthrometer testing not always correlate withfunctional outcome? (3) How can good long-term clinicalresults after repair of the posteromedial corner withoutrepair of the ACL (such as those reported by Hughston5) beexplained? and (4) What is the effect of an unrecognizedposteromedial corner injury on ACL reconstruction, andcan we compare it with that of an unrecognized postero-lateral corner injury?

Most orthopaedic surgeons would agree that a smallsubset of patients with ACL injuries could be treated non-operatively with excellent functional outcomes.3,12,15,18,21

Jackson et al12 reported on 21 of 62 untreated patientswith documented ACL injuries who had favorable clinicaloutcomes and described several people in the group whowere “functioning at a high level of competitive amateur orprofessional athletics” at a 10-year average follow-up. Inthis small subset, 10 of the 21 patients were noted to havecomplete ACL tears. With complete disruption of the ACL,one would wonder what allowed these patients to functionat such a high level without limitation. In addition to anexcellent rehabilitative effort, we believe that in thesepatients, significant posteromedial or posterolateral cornerinjury does not occur, and the dynamic capsuloligamentousstructures and an intact meniscocapsular complex main-tain the stability of the knee. In this way, purely isolatedfunction of the ACL seems to be discredited. This conceptis further strengthened by the reported lack of correlationbetween functional ACL reconstruction outcome and KT-1000 arthrometer measurements.23,25

In support of the stabilizing effect of the posteromedialcorner, Hughston5 reported on 41 patients who had acuterepair of the posteromedial capsuloligamentous con-straints. Of the 41 patients, 24 had ACL injuries, many ofwhich were not addressed according to accepted currentstandards. Nonetheless, at an average follow-up of 22years, the treatment provided good long-term results, andthe study focused attention on the functional significanceof the posteromedial corner structures. The importance ofthe “semimembranosus corner” has been emphasized oftenby Müller,20 who states, “As long as the semimembranosuscorner functions efficiently as a stabilizer, even a weak ordamaged cruciate ligament can function in a compensatedfashion. But if this stabilizing action is lost, the anteriorcruciate ligament alone is incapable of compensating andbecomes increasingly insufficient.”

Approaching the topic from the perspective of why ACLreconstructions fail, unrecognized, unaddressed cornerinjuries have been implicated.2,14,17,20 Just as ACL disrup-tion without significant “corner” (dynamic capsuloligamen-tous constraints and meniscocapsular complex) may resultin excellent functional outcomes without surgical inter-vention, dysfunction of the corner structures has beenassociated with failed ACL reconstructions and persistentrotatory instability.

Our purpose in this study was to draw attention to themedial and posteromedial knee structures and to describeassociated injury patterns. Although the cases reported are

Figure 12. During abduction stress testing with the knee in30º of flexion, elevation of the meniscus off the tibia, or“meniscal rise,” can be seen.


only a small percentage of the medial-sided knee injuriestreated by the senior author in this 6-year time period, webelieve that the extensive injury patterns described hereare significant. We have avoided the normal convention ofcalling all medial-sided knee injuries “MCL injuries”;instead, we described the injured anatomy. We believe theposteromedial corner structures play an integral role inresisting AMRI of the knee. When they are injured, theysometimes require repair. In our patients, 3 main injurypatterns with a POL injury common to all were discoveredthat revealed disruption of the semimembranosus complexas described by Müller.20 In theory, simple POL repairwould be restorative for some knees; yet, in others, reat-tachment of the semimembranosus or meniscotibial liga-ment may also be necessary. However, we believe thatbefore we can make recommendations regarding treat-ment, we must first prove that injuries to these structuresexist followed by further work ascribing functional signifi-cance.

In summary, there are 3 concepts with regard to medial-sided knee injuries that the authors believe to be impor-tant: (1) Not all medial-sided injuries are created equal; (2)the posteromedial corner structures, motored by the semi-membranosus, act in a dynamic fashion to resist AMRI;and (3) although less anatomically complex than the pos-terolateral corner, the posteromedial corner is no lessimportant functionally. The first is evidenced by thepathoanatomy in the patients described in our series, andthe second and third are based on previously publishedworks by Müller20 and Hughston and associates.5,6,8

For knee injuries with resultant functional instabilitysecondary to injury of the medial and posteromedial struc-tures accentuated by ACL disruption, treatment recom-mendations remain very subjective. The value of intra-articular ACL reconstruction has been firmly established,and it continues to be refined. However, we may come tofind that extra-articular reparative procedures can stillplay a role and have the potential to enhance functionaloutcomes in both isolated and combined injuries.

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