PCL injuries

Posterior cruciate ligament damage is often overlooked. Simon Ball and Fares Haddad explain the need for vigilance

Because posterior cruciate ligament (PCL) injuries are much less common than those to the anterior cruciate, we have a less thorough understanding of their management. Acute posterior cruciate ligament (PCL) injuries are often missed, possibly because of the examining physician’s lack of experience or because the patient does not appreciate the severity of the injury, and therefore delays seeking treatment.

Function The primary role of the posterior cruciate ligament is to prevent posterior translation of the tibia (sliding backwards) relative to the femur. The posterior cruciate ligament (PCL) provides 95% of this restraining force; the remaining 5% is from secondary restraints such as the posterolateral capsule, popliteus and the medial collateral ligament. The posterior cruciate ligament (PCL) also plays a secondary role in providing resistance at the knee joint to varus and valgus (inward and outward) forces, and to external rotation.

Anatomy

The posterior cruciate ligament (PCL) is approximately twice as strong and twice as thick as the ACL. Its average size in an adult is 13mm in diameter and 38mm in length. It originates from the anterolateral aspect (outer front surface) of the medial femoral condyle, and inserts into the rear of the tibia just below the joint line (see Figure 1: opposite above). The ligament may be partially separated into two bundles, the anterolateral (accounting for about 95% of the total ligament) and the posteromedial. In flexion the anterolateral bundle is tight and the posteriomedial bundle is lax. In extension these tensions are reversed.

How injuries occur

The reported incidence of acute posterior cruciate ligament (PCL) injuries varies widely, with studies showing anything from 2% to 40%. The average age at time of injury is 27.5 years, and it is generally those in their twenties and thirties who get injured(1). Isolated posterior cruciate ligament (PCL) injuries are usually caused by a direct blow to the front of the tibia while the knee is bent, forcing the backwards jolt of the tibia against the femur.

Sporting incidents are responsible for two out of five posterior cruciate ligament (PCL) injuries, second only to traffic accidents (which cause 45%). Specifically, motorcycle accidents (28%) and soccer-related injuries (25%) are the main culprits. In sport, the usual mechanism of injury is a fall on to the knee while the foot is plantar-flexed (see figure 2 opposite)(1). However, in Western countries, nearly all posterior cruciate ligament (PCL) damage (96.5%) occurs in combination with other ligament injuries(2).

Isolated rupture of the posterior cruciate ligament (PCL) leads to an increase in passive anterior and posterior or front-to-back movement in the medial compartment (inner area) of the knee. Logan et al(3)showed that on weight-bearing there is persistent subluxation (partial displacement) of the medial tibia throughout the extension-flexion arc. The femoral condyle persistently rides up the anterior slope of the medial tibial plateau, increasing the risk of early osteoarthritis. The kinematics of the lateral compartment of the knee are not altered by posterior cruciate ligament (PCL) injury(3).

Kumagai et al(4)also report increased patellofemoral forces after posterior cruciate ligament (PCL) rupture, associated with an increase in the posterior forces acting on the patella, especially the lower tip, which may increase the risk of patellofemoral pain and arthritis.

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Acute injury

Symptoms are often mild: the patient may regard the injury as a sprain and may not seek medical advice straight away. It is essential that therapists take a careful history and have a high index of suspicion, particularly when there has been a direct blow to the proximal (upper) tibia. In the acute stage there is variable swelling of the knee, which is painful and has a limited range of movement. The front of the knee may be bruised or lacerated. Over the next few days bruising may develop in the popliteal fossa from rupture of the posterior capsule. After a week or two patients may not have any pain.

Chronic injury

Patients may present with aching pain in the medial and patellofemoral compartments of the knee. They may or may not give a history of injury. There may be a feeling of instability but significant symptoms of giving way should lead you to suspect more complex injuries.

Examination

The classic test for posterior cruciate deficiency is the ‘posterior drawer test’, in which the knee is flexed to 90 degrees and the amount of backwards pull of the tibia against the femur is measured. The test may be repeated with the tibia in internal and external rotation. With an isolated PCL injury both internal and external rotation will decrease the amount of posterior translation at 90 degrees of knee flexion(5). If, however, the amount of posterior translation is increased, there may be concomitant posterolateral instability. The severity of injury is graded I to III, according to the extent of laxity.

The meniscofemoral ligaments (MFLs) act as secondary restraints, contributing 70% of the total resistance at 90 degrees of flexion in the PCL-deficient knee, compared to 28% in the normal knee(6). For this reason it is important also to assess the integrity of the MFLs, as this may affect your management plan.

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Other clinical tests of posterior cruciate injury are:

posterior sag sign: with the patient supine, hips and knees flexed at 90 degrees, the posterior ‘sag’ of the tibia is measured relative to the other leg.

quadriceps active test: the knee is flexed to 90 degrees and the thigh and foot stabilised. Contraction of the quadriceps will result in anterior translation of the tibia if there is disruption of the PCL(7).

It is essential to rule out associated ligamentous injuries to the posterolateral corner or the ACL, as these will indicate the need for reconstructive surgery.

Routine x-rays may show an avulsion fracture of the insertion of the PCL into the rear of the tibia. However, magnetic resonance imaging (MRI) gives the clearest results for posterior cruciate injuries. In isolated acute PCL injuries it has a sensitivity and specificity of more than 90%(8)with some studies reporting both sensitivity and specificity as 100%(9).

MRI is also useful in assessing the healing of a PCL injury – although some caution is needed here. Recent reports suggest that up to 93% of partial or complete PCL ruptures may regain continuity: the ligament joins up again so that it appears intact on MRI scanning, even if it does not work properly(10,11). It is probably for this reason that MRI is less reliable at diagnosing chronic PCL injuries: 43% of the time in chronic cases the ligament will appear to be uninjured(12).

The use of arthroscopy in assessment is controversial and many believe that good clinical examination and MRI are sufficient to make the diagnosis and plan management. Others believe arthroscopy may provide information valuable to long-term management. One advantage of general anaesthesia is that it allows the surgeon to carry out a full examination of the knee. Disadvantages include the risk of compartment syndrome. A major pitfall is the inaccurate diagnosis of an anterior cruciate injury, where apparent laxity of that ligament is the result of PCL injury.

Treatment

Recently there have been several reports on the natural history of isolated ruptures of the PCL. Shelbourne et al(13)performed a prospective study of 271 patients with isolated PCL injury who were treated non-operatively. They evaluated participants using two subjective knee surveys and an activity survey. The subjective scores of patients with acute, isolated PCL injuries did not correlate with the seriousness of their knee laxity. Nor was it possible to identify any characteristics that might determine which patients among this group would have deteriorating knee function.

Another study on the non-operative treatment of PCL injuries in athletic patients reports that, irrespective of the extent of laxity, half of the group returned to the same sport at the same or higher level, one-third returned to the same sport at a lower level, while one in six did not return to the same sport(14).

Where the tear is mid-ligament, acute isolated PCL injuries may heal(11), a compelling reason why many authors believe that most, if not all, of these injuries should be treated conservatively(15). Surgery should be reserved for extreme cases, where there are problems with instability. In such instances it is likely that there is concomitant injury of secondary restraints, such as the posterolateral corner. These injuries must be identified, and, in complex cases, surgery may be the best course.

Where the insertion of the PCL into the tibia has avulsed (broken off at the bone), early operative treatment is advisable.

Non-operative management of isolated PCL injury involves immobilisation in a knee brace for six weeks, after which the patient may start rehab: isolated training of the quadriceps, hip and core stability muscles. Hamstring strengthening should be avoided in the early stages as this increases the posterior load on the tibia and accentuates the anterior subluxation of the femur.

Reconstruction

Operative repair may be either open or by arthroscopic keyhole procedures. Most reconstructions involve a ‘single-bundle’ technique, which aims to replace the strong anterolateral bundle of fibres. But there are now ways to replace both the anterolateral and posteromedial bundles. Several different types of graft material may be used.

Over the past five years, we have favoured the arthroscopic technique and used a double-bundle reconstruction, recreating the anterolateral and posteromedial bundles by using two femoral tunnels.

Conclusion

Although isolated PCL injuries are rare, it is important that athletes and physicians remain on the lookout, to avoid missing the diagnosis. Current research suggests that isolated acute injuries should be treated conservatively, but improved techniques may make surgery the treatment of choice in the future.

References

1. Schulz, MS, Russe, K, Weiler, A, Eichhorn, HJ, Strobel, MJ ‘Epidemiology of posterior cruciate ligament injuries’. Arch Orthop Trauma Surg.2003; 123(4): 186-91.

2. Fanelli, GC, Edson, CJ ‘Posterior cruciate ligament injuries in trauma patients: Part II’. Arthroscopy1995; 11(5): 526-9.

3. Logan, M, Williams, A, Lavelle, J, Gedroyc, W, Freeman, M ‘The effect of posterior cruciate ligament deficiency on knee kinamatics’. Am J Sports Med.2004; 32(8): 1915-22.

4. Kumagai, M, Mizuno, Y, Mattessich, SM, Elias, JJ, Cosgarea, AJ, Chao, EY. ‘Posterior cruciate ligament rupture alters in vitro knee kinematics’. Clin Orthop Relat Res.2002; 395: 241-8.

5. Bergfeld, JA, McAllister, DR, Parker, RD, Valdevit, AD, Kambic, H ‘The effects of tibial rotation on posterior translation in knees in which the posterior cruciate ligament has been cut’. J Bone Joint Surg Am. 2001; 83-A(9): 1339-43.

6. Gupte, CM, Bull, AMJ, Thomas, RD, Amis, AA ‘The meniscofemoral ligaments: secondary restraints to the posterior drawer’. J Bone Joint Surg Br. 2003; 85-B: 765-73.

7. Daniel, DM, Stone, ML, Barnett, P, Sachs, R ‘Use of the quadriceps active test to diagnose posterior cruciate-ligament disruption and measure posterior laxity of the knee’. J Bone Joint Surg Am. 1988; 70(3): 386-91.

8. Rubin, DA, Kettering, JM, Towers, JD, Britton, CA ‘MR imaging of knees having isolated and combined ligament injuries’. AJR Am J Roentgenol. 1998; 170(5): 1207-13.

9. Gross, ML, Grover, S, Bassett, LW, Seeger, LL, Finerman, GAM ‘Magnetic resonance imaging of the posterior cruciate ligament: clinical use to improve diagnostic accuracy’. Am J Sports Med 1992; 20: 732-7.

10. Boks, SS, Vroegindeweij, D, Koes, BW, Hunink, MG, Bierma-Zeinstra, SM ‘Follow-up of post traumatic ligamentous and meniscal knee lesions detected at MR imaging: systematic review’. Radiology 2006; 238(3): 863-71.

11. Shelbourne, KD, Jennings, RW, Vahey, TN ‘Magnetic resonance imaging of posterior cruciate ligament injuries: assessment of healing’. Am J Knee Surg. 1999; 12(4): 209-13.

12. Servant, CT, Ramos, JP, Thomas, NP ‘The accuracy of magnetic resonance imaging in diagnosing chronic posterior cruciate ligament injury’. Knee2004; 11(4): 265-70.

13. Shelbourne, KD, Muthukaruppan, Y ‘Subjective results of nonoperatively treated, acute, isolated posterior cruciate ligament injuries’. Arthroscopy 2005; 21(4): 457-61.

14. Shelbourne, KD, Davis, TJ, Patel, DV. ‘The natural history of acute, isolated, nonoperatively treated posterior cruciate ligament injuries. A prospective study’. Am J Sports Med. 1999; 27(3): 276-83.

15. Dowd, GS ‘Reconstruction of the posterior cruciate ligament. Indications and results’. J Bone Joint Surg Br.2004; 86-B: 480-91.