Medial and lateral collateral ligament injuries of the knee

                     Medial and lateral collateral ligament injuries of the knee

                 

                                                            Dr KS Dhillon FRCS

Anatomy of the collateral ligaments

There are two collateral ligaments, one on either side of the knee. The one on the medial side is referred to as the medial collateral and and the other on the lateral side is referred to as the lateral collateral collateral ligament.

Medial collateral ligament

The medial collateral ligament (MCL) has two components, the superficial and the deep components.
The superficial medial collateral ligament has one femoral and two tibial attachments and is the largest structure on the medial aspect of the knee[1]. The proximal femoral attachment is at a round to oval depresion about 3.2 cm proximal and 4.8 cm posterior to the medial femoral epicondyle[1]. There is no attachment between the superficial and deep collateral.
There are two distal attachments of superficial medial collateral ligament.
The attachment of the proximal of the two distal attachments is mainly to soft tissues especially to the anterior arm of the semimembranosus and the distal component has bony attachment anterior to the posteromedial crest of the tibia. The distal component forms the posterior floor of the pes anserine bursa and it also blends with the semimembranosus tendon[1]. Between the two distal attachments pass the inferior medial genicular artery and vein, along with its corresponding nerve branch from the tibial nerve. The average overall length of the superficial medial collateral ligament is  between 10 and 12 cm[1].
The deep medial collateral is formed by thickening of the medial capsule of the knee and it is clearly seen along its anterior border where it is parallel to the superficial collateral. Posteriorly it merges with the central arm of the posterior oblique ligament. It consists of the proximal meniscofemoral and the distal meniscotibial component. It is attached to the meniscus at the joint level and to the medial femoral condyle proximally and the medial tibial plateau distally[1].
The lateral collateral ligament (LCL) is part of a complex of ligaments at the  posterolateral corner of the knee. This complex consists of the LCL, the arcuate ligament, the popliteus ligament, the popliteofibular ligament, the, the short lateral ligament, and the posterolateral joint capsule. Unlike the MCL the LCL is separated from the lateral meniscus by a fat pad.
There appears to be little consensus in the literature regarding the bony attachments of the lateral (fibular) collateral ligament (FCL). Cadaveric dissections and review of the literature by Chappell et al [2] showed that in about half of the instances the proximal attachment is at the apex of the lateral epicondyle and in the other half the attachment is posterior and proximal to the LE. The distal attachment is to lateral aspect of the fibular head by two or three bands [2].The average length of the ligament is about 48.3 mm and the average width is about 4mm [2]. There is a wide variation in the dimensions of the length of ligament reported in the literature varying from 35mm to 72mm [3].

Collateral ligament injuries

Collateral ligament injuries are caused by excessive varus or valgus force applied on the knee with a varus force producing a LCL injury and a valgus force causing a MCL injury. Most patient are able to walk after such injuries and the pain is localised to the medial or the lateral side of the knee. Collateral ligament injuries usually do not produce mechanical (pop, locking) symptoms or symptoms of knee instability. Swelling is usually present over the area of injury and redness may appear after a few days.
Examination shows localised tenderness and swelling at the site of the injury. Tenderness at the proximal or distal attachment may indicate an avulsion injury of the ligament.
Valgus stress testing with the knee in 25-30 º flexion would show laxity when the MCL is torn and varus stress testing with the knee in 20-25 º of flexion would show laxity if the LCL is torn. Laxity on the medial side with knee in extension would indicate a tear of the anterior cruciate ligament (ACL) in addition to the MCL tear. A laxity on the lateral side with the knee in extension would indicate a tear of the posterior capsule and other lateral structures in addition to the LCL tear.
The severity of ligament injury is clinically graded from I to III:

• Grade I - Less than 5 cm laxity (partial tear)
• Grade II - 5-10 cm laxity
• Grade III - More than 10 cm laxity (complete tear)

The diagnosis of collateral tears is always clinical. An X-ray of the knee should however be done to exclude a bony avulsion of the ligament. A varus and valgus stress X ray can be useful for demonstrating ligament laxity. An MRI is usually not needed to make a diagnosis of collateral ligament injury.
An MRI is not very reliable for differentiating grades of injury. Grade 1 injuries usually show periligamentous edema, grade II injuries show partial disruption of the ligamentous structures and grade III injuries show complete disruption of the ligament[4].

Treatment of collateral ligament injuries

All three grades of isolated collateral ligament injuries can be treated conservative with good results. Initially treatment includes cryotherapy, elevation and compression to reduce pain and swelling. Grade I injuries can be treated without a brace while grade II and III injuries are treated with brace and early mobilization. Muscle strengthening exercise are carried out in all patient with ligament injury. The injuries require about 4 to 6 weeks to heal. It may take longer for grade III injuries.
Derscheid et al [5] reported a return to unprotected sports, of football players with Grade I MCL sprains, after an average of 10.6 days and those with grade II sprains after 19.5 days.
Jones et al [6] reported achieving a stable knee in 22 out 24 high school football players with isolated Grade III injuries of the MCL, with conservative treatment. The average recovery time in these patients was 29 days. The players returned to competitive sports at a mean time of 34 days. Similar good outcome of conservative treatment of grade III MCL injuries have been reported by other authors [7,8].
Studies comparing conservative and surgical treatment of grade III MCL tears show that there is no subjective or objective differences between the surgically and non-surgically managed group [9,10]. Bony avulsion injuries, however, benefit from surgical intervention [11].
Chronic valgus instability may result when grade III MCL injuries are inadequately treated and fail to heal. Such instability which affect activities of daily living and affect inability to participate in athletic activities would be an indication for surgical treatment.
Lateral collateral injuries are rare [12] and there is scarcity of literature on the treatment of LCL injuries [13]. Good functional outcome of conservative treatment of grade I and grade II injuries has been reported [14,15]. The numbers of patients in these studies has been very small. Surgery is usually recommended for grade III  posterolateral knee injuries with acute repair of avulsed structures, reconstruction of midsubstance tears [16]. However the number of cases in the published reports has been small and the evidence is therapeutic Level IV evidence. There is a lack of publications comparing operative versus non-operative treatment of grade III LCL injuries. Grade III injuries are often associated with tears of the cruciate ligament which makes treatment more complicated.

Long term outcome of collateral injuries

There is a paucity of literature on the long term outcome of treatment of collateral ligament injuries of the knee.
In 1996 Lundberg and Messner [17] published the long term outcome of treatment of partial medial collateral ligament ruptures. They prospectively followed up 38 patients with partial tears of the MCL. The patients were seen at 3 months, 4 years, and 10 years after the initial trauma. Clinical and radiological examination was carried out. At 4 years follow up the median  Lysholm score was 100 (range, 64 to 100) and 87% of the patients had normal knee function during strenuous activities. At 10 years, the median Lysholm score was 95 (range 73 to 100) and the patients continued to performed on a similarly high activity level as at 4 years. Early signs of osteoarthritis was seen in 13% of the patients but none had joint space reduction.
In 1997 Lundberg and Messner [18] published the 10 years outcome of treatment of isolated and combined medial collateral ligament ruptures. They studied a matched-pair of 40 patients with acute isolated partial medial collateral ligament injury and acute combined medial collateral and anterior cruciate ligament injury. All patients in the first group were treated conservatively and the later group were treated by repair of both ligaments. At 10 years follow up both group of patients had similarly high knee functional Lysholm score and similar activity levels (recreational team sports). There was residual laxity in patients with combined injury. Post traumatic osteoarthritis (OA) was present in half of the knees with combined injuries. There was no OA in patients with isolated injuries. Although the long term functional outcome was good in both groups of patients, the patients with combined injuries had more repeat injuries and more repeat surgeries, increased sagittal laxity, and a higher incidence of radiographic osteoarthritis.
Kannus [19] in 1989 published an average of 8 years follow up of 11 patients with Grade II sprains and 12 patients with Grade III sprains of the lateral collateral ligament who were treated conservatively. He found that the result in Grade II sprains was generally good, despite the fact that some residual laxity persisted. On the other hand in Grade III sprains, the results were not  so good with a high incidence gross lateral laxity, ACL insufficiency, muscle weakness, and posttraumatic osteoarthritis of the injured knee.

Conclusion

The collateral ligaments are the medial and lateral static stabilizers of the knee against varus and valgus stress. The medial collateral injury is the commonest ligament injury to the knee. The ligament injuries are graded into three depending on its severity.Grade I and II injuries are treated conservatively and healing is usually good because of the good vascularity around the ligaments and long term outcome of such injuries is good.
There is controversy, however, with regards to the treatment of grade III injuries. Such injuries are often associated with injury to other structures around the knee and surgical treatment is often recommend. The long term outcome of treatment of grade III injuries is not very good with patients having residual laxity, muscle weakness and OA of the knee in some instances. There is, however, paucity of literature on the long term outcome of treatment of collateral ligament injuries of the knee especially in the recent years.

References

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18. Lundberg M, Messner K. Ten-year prognosis of isolated and combined medial collateral ligament ruptures. A matched comparison in 40 patients using clinical and radiographic evaluations. Am J Sports Med. 1997 Jan-Feb;25(1):2-6.
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