Twist and turn

A 25 year old professional football player presented to an orthopaedic clinic reporting knee instability, especially on turning. He said that five weeks ago he had been playing when he suddenly heard a snap after changing direction. His knee was slightly flexed when it happened, and it immediately got swollen. Afterwards, he was not able to continue playing. The examination showed some effusion, along with positive Lachman and pivot shift tests. Other tests proved negative.

Fig 1

Questions

1. What is your differential diagnosis?
2. What additional diagnostic investigations would be important in this case?
3. What does the picture show?
4. What is the treatment of choice for this patient?

Answers

1. Doctors should suspect a partial or complete tear of the anterior cruciate ligament when a patient describes a combination of non-contact twisting, a "snap" sound, and immediate swelling with knee instability. Positive results in both the Lachman and pivot shift tests make the diagnosis likely. This is also often associated with injuries to the medial collateral ligament, meniscal cartilage, or articular cartilage. In this patient, however, direct signs are lacking.
2. Medical resonance imaging is the first choice for confirmation of a tear of the anterior cruciate ligament. It detects complete and meniscal tears with an average accuracy of 90% and 80-90%, respectively. Since the diagnosis of a torn anterior cruciate ligament is mainly a clinical one, doctors could skip magnetic resonance imaging and do direct invasive and therapeutic arthroscopy instead. Arthroscopy assesses the hyaline cartilage through direct visualisation.¹
3. A magnetic resonance image was got to confirm the diagnosis and to look for associated injuries. The sagital view showed that, compared with the posterior cruciate ligament, the anterior ligament was much thinner. Only a residual thin black structure surrounded by grey synovium was observed (fig 1).The picture is compatible with a nearly complete rupture of the anterior cruciate ligament. Other images showed no sign of associated injuries.
4. Treatment options are either non-operative management or reconstructive surgery. Non-operative management includes physical treatment and brace wear. The surgical repair of a torn anterior cruciate ligament includes the arthroscopic removal of the damaged ligament and replacement with the middle third of the patellar or hamstring tendons.

Being a professional athlete wishing to resume competitive sport, the patient was advised to undergo reconstructive surgery (figs 2 and 3).

Discussion
The anterior cruciate ligament is an intra-articular extrasynovial structure that extends from the anterior intercondylar region of the tibia to the inner aspect of the lateral femoral condyle. It limits anterior translation of the tibia in relation to the femur, stabilises the knee in extension and prevents hyperextension, and prevents excessive internal rotation.

This ligament is the most often injured ligament in the knee.² Injuries often occur in contact sports like football and American football, or non-contact sports like skiing or athletics. There is normally a history of a twisting injury accompanied by a tearing feeling and subsequent effusion.

Fig 2

Fig 3

After a history suggesting an injury to the anterior cruciate ligament, doctors should do a clinical examination incorporating different tests. In the Lachman test, the patient must lie flat with the knee flexed to about 20 degrees (fig 4). One hand should fixate the thigh, while the other pulls the leg towards you, just like when opening a drawer. In case of a positive test (rupture of the ligament), the tibia is displaced towards you, and so it becomes possible to "open the drawer." In normal circumstances, the ligament works like a padlock preventing the tibia from being displaced, so the "drawer" in this case remains shut, and no movement is elicited.

This test uses the same principle as the anterior drawer test, but an important difference in this case is that the knee is flexed to a right angle. The Lachman test uses a smaller angle to lessen the opposition of the hamstring muscles, whose tone will be decreased with smaller angles.

Fig 4

The pivot shift or jerk test reproduces the natural movements used in sports like football or basketball, which are required for changing directions (called cutting movements). Firstly, you should push the top extremity of the tibia (upper end of the leg) forward (fig 5). This movement should be elicited in the same direction and way as the drawer test, but here you are trying to "open the drawer" by using one hand to push it through the back, and not pulling it through the front. At the same time, you should rotate the foot internally using your other hand, and apply a valgus (bending outward) force. While in this position, the next step is to extend and flex the knee. When the test is positive for rupture of the ligament, this will sublux and then reduce the tibia to its correct position on the femur, originating a visible or palpable clunk or jerk at about 30° of flexion of the knee.

No single test or study is 100% accurate. The orthopaedic surgeon will, therefore, have to resort to a combination of history, physical examination, and further diagnostic studies to make the diagnosis.

A patient with a torn anterior cruciate ligament may experience recurrent instability and early joint damage. The degree of instability depends on the physical load exerted on the knee, the strength of the quadriceps and hamstring muscles, as well as in the extension of the damage to the ligament and other structures of the knee.

The final decision for surgical treatment is based on multiple factors, including the degree of instability, the patient's sporting demands, and eventual further knee damage.

The patient should begin intensive physical therapy a few days after the surgery and the recovery process encompasses four distinct phases.

The first phase (6-8 weeks) aims to increase flexion to 135º, decrease swelling, and increase muscle tone. In the second phase (six weeks), the goal is to regain the full range of motion and to improve the performance of the activities of daily living. The third phase (three months) should see a gradual return to sporting activities. After six months, the athlete should be able to perform cutting and pivoting movements, as well as taking parts in normal sports activities. The fourth phase of recovery is sport specific. The athlete is expected to increase their sport specific activities and endurance which will allow them to reach a fitness compatible with the demands of professional sport. It is important to stay motivated and to have a physiotherapist help during all stages of the recovery process.

M G H van de Sande, sixth year medical student, Academic Medical Centre, Amsterdam, Netherlands

M J H Ariës, sixth year medical student, University Medical Centre, Nijmegen, Netherlands
Email: m.aries@student.kun.nl

C P van der Hart, orthopedic surgeon, OLVG Hospital, Amsterdam


studentBMJ 2004;12:265-308 July ISSN 0966-6494

1. Bohnhof K, Imhof H, Pope TL. Musculoskeletal imaging. Stuttgart: Thieme, 2001:108-12.
2. Heeg M. Letsels van het bekken en de onderste extremiteit. In: Verhaar JAN, Linden van der AJ. Orthopedie. Houten: Bohn Stafleu van Loghum, 2003:160-3.