Working Diagnosis:
Right patellar tendon rupture

Treatment:
Initially, ice and knee immobilizer. Ultimately, primary right infrapatellar tendon surgical repair.

Outcome:
Successful surgical repair without complications. Postoperatively placed in a hinged knee brace locked in extension with the ability to unlock and flex to 30 degrees for riding in vehicle but locked in extension at all other times for the first two weeks. Sutures removed at two weeks and patient has begun physical therapy with the goal of reaching 90 degrees flexion by six weeks from surgery.

Author's Comments:
The true incidence of patellar tendon rupture is not known, but this injury is observed less frequently than rupture of the quadriceps tendon and usually occurs in those younger than 40 years. It is the third most common injury to the extensor mechanism of the knee, following patellar fracture and quadriceps tendon rupture.
Rupture of the patellar tendon usually occurs at the osseotendinous junction and causes complete derangement of the knee extensor mechanism. If the tendon does not heal properly and at the correct length and tension, knee range of motion and strength can be altered significantly, leading to early fatigue, patellofemoral pain, and, possibly, instability, which can thereby prevent return to preinjury status.
The typical mechanism is a sudden eccentric contraction of the quadriceps, usually with the foot planted and the knee flexed as the person falls. The estimated force required to disrupt the extensor mechanism has been reported to be as high as 17.5 times body weight. Given that considerable force is needed to rupture a healthy tendon, it is likely that ruptures occur in areas of preexisting disease. For example, ruptures may occur after local injection of corticosteroid near the inferior pole of the patella as treatment for patellar tendinitis. This complication, first reported in 1969 by Ismail et al and later elucidated by Kennedy et al, is probably a result of steroid-induced breakdown of collagen organization and strength. In a series by Kelly et al, nearly 60% of patients who sustained patellar tendon ruptures had received an average of two or three steroid injections around the patellar tendon before rupture.
Complications of an untreated rupture to the extensor mechanism can be extremely disabling. Surgical intervention allows for excellent recovery of motion and strength, provided that the injury is diagnosed in a timely fashion and repaired immediately.

Editor's Comments:
This case is a good example of why you want to do a thorough exam even in the situation where there is swelling and pain complicating the examination. Palpating the tendons above and below the patella as well as checking strength are key to making the diagnosis based on the physical exam and leading to urgent imaging and timely orthopedic referral. Surgery within 7 days is ideal.

References:
- Kelly DW, Carter VS, Jobe FW, Kerlan RK. Patellar and quadriceps tendon ruptures--jumper's knee. Am J Sports Med. Sep-Oct 1984;12(5):375-80.

- Ramseier LE, Werner CM, Heinzelmann M. Quadriceps and patellar tendon rupture. Injury. Jun 2006;37(6):516-9

- Matava MJ. Patellar Tendon Ruptures. J Am Acad Orthop Surg. Nov 1996;4(6):287-296.

- Kuechle DK, Stuart MJ. Isolated rupture of the patellar tendon in athletes. Am J Sports Med. Sep-Oct 1994;22(5):692-5

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