Patellar Tendon Ruptures
Matthew J. Matava, MD and Sue Million, MHS, PT

Background
Rupture of the patellar tendon is a relatively uncommon injury, occurring primarily during athletic pursuits in patients younger than 40 years. Most of these injuries are unilateral, although bilateral ruptures have been described in patients with systemic illnesses known to weaken collagen structures. Technically, the term “patellar tendon” is a misnomer because the tendon is actually a ligament connecting the patella and the tibial tubercle. However, this term is widely accepted because the patella is technically a sesamoid bone merely encompassed by the thickened condensation of the quadriceps tendon.

Anatomy and Biomechanics
The patellar tendon comprises the thickened fibers of the rectus femoris tendon that traverse the anterior surface of the patella. It converges medially and laterally, with the extensor retinaculum proximal to its insertion into the tibial tubercle. This relationship is important because rupture of the tendon usually involves the retinaculum as well.

The greatest force in the tendon is generated during active knee extension with the joint at approximately 60 degrees of flexion. It has been shown that the tensile strain in the tendon is much higher at the bony insertion sites than in the tendon’s midsubstance. Collagen fiber stiffness is also decreased at these peripheral regions. These differences in force transmission may explain why rupture occurs most commonly near the proximal insertion rather than in the midsubstance.

Etiology
Rupture is invariably caused by a forceful quadriceps contraction against a fixed structure or by a sudden load of the patient’s body weight against an actively contracting quadriceps. The common denominator in both of these modes of injury is an eccentric quadriceps contraction with muscle lengthening during the contraction.

Acute patellar tendon rupture usually occurs when there is long-standing tendon degeneration. Pathologic findings include hypoxic and calcifying tendonopathy, mucoid degeneration, and tendolipomatosis. Patients with preexisting systemic disorders such as diabetes mellitus, chronic renal failure, and various autoimmune conditions are susceptible to tendon rupture during nonstrenuous activity. These ruptures are occasionally bilateral because of the overall weakened state of the collagenous tissues.

Rupture may also occur after the injection of a corticosteroid medication in or around the tendon. We recommend against corticosteroid injection in or around the patellar tendon. These medications are known to cause necrosis and disorganization of the collagen fibrils, resulting in a weakened structure.

Patellar tendon rupture can also occur after surgical procedures that disturb the extensor mechanism of the knee, such as total knee arthroplasty or ACL reconstruction with harvest of the central third of the patellar tendon. In these situations, the rupture tends not to disrupt the reconstructive procedure, but the long-term outcome varies because of the alteration in the anatomy and the necessity of reconstructive grafts to reestablish knee extension when local tissues are deficient.

Clinical Evaluation
Physical Examination
After an acute injury, the patient usually has a tense hemarthrosis of the knee and cannot bear weight on the involved extremity. Active knee extension is usually impossible, especially if the rupture extends into the medial and lateral retinaculi. Active knee flexion, although possible, is limited because of pain. A gap may be palpable at the rupture site, and the patella may feel proximally displaced because the unopposed pull of the quadriceps muscle. Associated intra-articular injuries (such as an ACL tear) may occur and must also be ruled out.

Radiographic Evaluation
Plain radiographs usually are the only imaging modality required to confirm the diagnosis of an acute rupture.
The most common finding is a high-riding patella (patella alta), which is noted best on the lateral view.
Occasionally, one or more bony fragments are attached to the tendon if the injury resulted from an avulsion.
High-resolution ultrasonography has also been used effectively to confirm both acute and chronic ruptures. Sagittal images obtained with a linear array transducer allow identification of a confluent area of hypoechogenicity, signifying a complete rupture. With chronic tears, thickening of the tendon along with disruption of the normal tendon echo pattern is seen. Ultrasonography, although inexpensive and easy to perform, is operator dependent, which results in accuracy rates occasionally differing between institutions.

MRI has emerged as an excellent, although expensive, means of evaluating the extensor mechanism. With rupture, tendon discontinuity is seen along with waviness of the tendon ends and hemorrhage in the intervening space. This imaging modality is also helpful in evaluating the knee for concomitant intra-articular injuries.

Classification
Patellar tendon ruptures have been classified based on the location, configuration, and chronicity of the tear, but no universally accepted classification system currently exists. The most widely used system is that of Siwek and Rao (1981), who grouped ruptures into two categories based on the interval between injury and repair: immediate versus delayed (repair more than 2 weeks after injury). This system is the only one that has successfully correlated the type of rupture with the method of treatment (primary repair versus tendon reconstruction) and final outcome. The difference in rehabilitation between the two types of rupture is affected most by the method of treatment rather than by the type of rupture.

Treatment
Surgical repair of the ruptured patellar tendon is required for optimal function of the extensor mechanism of the knee. There is no place for nonoperative treatment of this injury. Surgical repair should be done as soon after the injury as possible. Multiple methods for repair have been described, although simple end-to-end repair, with or without a reinforcing cerclage suture, has been the method most commonly used.

With a chronic rupture (more than 6 weeks), simple reapproximation of the tendon ends is often impossible because of contraction of the quadriceps muscle and resulting proximal patellar migration. In this situation, preoperative patellar traction and passive ROM exercises are necessary.

A number of reconstructive procedures have been used after the reestablishment of knee motion: primary repair combined with autogenous graft augmentation with the hamstring tendons or fascia lata, inert carbon fiber or nonabsorbable tape suture repair, and allograft tissues in the form of the Achilles tendon or an intact patellar tendon.

Rehabilitation after Repair of Patellar Tendon Rupture
General Principles
Successful rehabilitation after patellar tendon repair requires an integration of the concepts of tissue healing and biomechanics with muscle strengthening and conditioning techniques. Essential to optimal recovery is early joint mobilization, gradual introduction of forces across the patellar tendon, normalization of movement, and progressive quadriceps strengthening. The ideal program uses a multiphase approach that includes functional rehabilitation strategies to allow the full resumption of activities of daily living and return to sport. The following protocol is designed for the rehabilitation of an acute, unilateral tendon repair.

Termination of Rehabilitation
Rehabilitation is terminated when the patient demonstrates full joint ROM and 85 to 90% of contralateral lower extremity strength on isokinetic testing. Resumption of strenuous athletic activity is prohibited for 4 to 6 months.

In addition to isokinetic testing, a functional assessment of lower extremity performance is recommended before return to sport. The one-legged hop test for distance should be included as a way to compare lower extremity functional capacity and assess readiness to return to previous activity.

An athlete should display symmetrical movement patterns and normal static alignment before release to sport.