eMedicine Specialties > Orthopedic Surgery > Knee

Patellar Tendon Rupture

Author: Christopher C Annunziata, MD, Orthopedic Surgeon, Commonwealth Orthopedics and Rehabilitation; Assistant Clinical Professor, Department of Orthopedic Surgery, Georgetown University Medical Center; Team Physician, Washington Redskins; Team Physician, DC United
Coauthor(s): Elizabeth Ignacio, MD, Associate Clinical Professor, Department of Orthopedic Surgery, John A Burns School of Medicine, University of Hawaii; Consulting Sports Medicine Orthopedic Surgeon, University of Hawaii Athletic Department
Contributor Information and Disclosures

Updated: Sep 25, 2009

Introduction

The patellar tendon ruptures relatively infrequently. However, the 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. The focus of this article is acute patellar tendon ruptures, especially those associated with acute sports-related injuries. Patellar tendon ruptures also can occur as a complication of total knee arthroplasty,¹ anterior cruciate ligament (ACL) reconstruction using the patellar tendon as an autograft,² or excision of chronic tendinosis. However, the etiology and treatment in these circumstances are beyond the scope of this article.

The images below depict defects of the patellar tendon.

History of the Procedure

In the past, the surgical technique for acute rupture of the patellar tendon was primary suture repair. Augmentation of the repair was believed to be necessary and was achieved using a cerclage of wire, suture, or autogenous graft such as the semitendinosus in order to reinforce the repair. Routinely, the knee was kept locked in extension for up to 6 weeks to prevent undue stress on the repair.

Earlier and more aggressive rehabilitation techniques are now available. Krackow introduced a novel interlocking stitch technique,⁵ and Marder and Timmerman demonstrated that repair alone is equally as durable without augmentation.⁶

Problem

The patellar tendon serves as the distal extent of the quadriceps insertion. Rupture of the patellar tendon usually occurs at the osseotendinous junction and causes complete derangement of the knee extensor mechanism. This is a disabling injury in the active person, resulting in an inability to actively obtain and maintain full knee extension. 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. Immediate surgical repair is recommended for optimal return of knee function and power.

Frequency

The true incidence of patellar tendon rupture is not known, but it 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.^7,8

Etiology

Patellar tendon rupture often occurs in the setting of long-standing patellar tendon irritation. The rupture is the final result of chronic tendon degeneration due to repetitive microtrauma. Histopathologically, ruptured tendons studied by Kannus et al demonstrated changes consistent with chronic inflammation and degeneration.⁹

Ruptures also have been known to occur after local injection of corticosteroid near the inferior pole of the patella as treatment for patellar tendinitis (ie, jumper's knee). This complication, first reported in 1969 by Ismail et al¹⁰ and later elucidated by Kennedy et al,¹¹ 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 2-3 steroid injections around the patellar tendon prior to rupture.^12,1

Patellar tendon rupture is usually unilateral and is the result of a traumatic athletic injury. The typical mechanism is a sudden eccentric contraction of the quadriceps, usually with the foot planted and the knee flexed as the person falls. However, in the setting of systemic inflammatory disease, diabetes mellitus, or chronic renal failure, bilateral ruptures can occur with lower-energy stress.^13,14,15,16 Additionally, patellar tendon ruptures can result form a posterior knee dislocation.¹⁷

Systemic disorders are related to an increased incidence of tendon ruptures. Pritchard et al found that tendon ruptures in systemic lupus erythematosus (SLE) appear to be associated with extended disease duration, chronic corticosteroid therapy, evidence of steroid-induced musculoskeletal complications, minimal disease activity at the time of rupture, and deforming hand arthropathy.¹⁸

Inflammatory changes have been noted at the site of rupture in patients with SLE,¹⁹ amyloid deposition has been noted at the site in patients with chronic renal failure undergoing dialysis,²⁰ and elastosis has been noted in patients with chronic acidosis.²¹

Anatomically, the patellar tendon tends to tear in the mid substance in patients with systemic disease, rather than at the osseotendinous junction, as typically occurs in acute traumatic injury. After a tear of the mid substance, tendon repair and rehabilitation can be especially difficult and is exacerbated further by the preexisting comorbid condition.

Patellar tendon ruptures also can occur following surgery for total knee arthroplasty, procedures using the central third of the patellar tendon as an autograft, or excision of patellar tendinosis.

Pathophysiology

Unilateral traumatic ruptures of the patellar tendon tend to occur when a violent contraction of the quadriceps is resisted by the flexed knee (eg, while landing after a jump). The estimated force required to disrupt the extensor mechanism has been reported to be as high as 17.5 times body weight. In the flexed knee position, the patellar tendon sustains greater stress than the quadriceps tendon, and the tensile load is much higher at the insertion sites than in the mid substance of the tendon. Therefore, the patellar tendon most commonly ruptures near its proximal end, off the inferior pole of the patella.

Since considerable force is needed to rupture a healthy tendon, it is likely that ruptures occur in areas of preexisting disease.

Presentation

History, physical examination, and standard radiographs typically are adequate for making a diagnosis of acute patellar tendon rupture.

Disruption of the patellar tendon is associated with immediate, disabling pain. Acute rupture frequently results in an immediate 'pop' or tearing sensation. The patient usually notes immediate swelling and difficulty rising and bearing weight following the injury.

On physical examination, diffuse swelling in the anterior knee with ecchymosis, hemarthrosis, and patella alta is observed. Tenderness exists along the anterior knee and retinacula, and a defect at the level of the rupture is usually palpable (see image below), although significant swelling can make this difficult to appreciate initially. The patella may also feel proximally displaced, compared with the contralateral side.

Occasionally, a deceleration injury can cause a disruption of the extensor mechanism. In this setting, it is also important to assess both the integrity of the meniscal cartilage with palpation of the joint line and the ACL with a Lachman test.²²

If the diagnosis of tendon rupture is delayed, scar tissue may obliterate what previously had been a palpable defect. In this scenario, some degree of active extension may be possible, but with weakness and some degree of extensor lag. Quadriceps atrophy may also be noted, with considerable weakness, especially with weightbearing, stair climbing, and rising from a seated position. The weakness can exist to such a degree that the patient performs a forward thrusting motion of the limb in the swing phase of gait and complains of stance instability.

Indications

Early diagnosis and definitive treatment provide the best results. The type of treatment depends predominantly on the extent of the tear. The most common injury involves the acute, complete disruption of the tendon, and subsequent dysfunction of the extensor mechanism. In this setting, surgical repair is the treatment of choice. In general, repair should be performed as soon as possible after the injury to limit the degree of quadriceps atrophy and prevent any contractures that might make the procedure more difficult.

In some situations, a partial tear of the patellar tendon may occur. The patient may be able to maintain full, active extension and normal patellar height. This individual can potentially be treated nonoperatively with immobilization until the tendon has healed. However, one must be certain that the tear is, in fact, partial before initiating this program. An MRI may be useful in this situation (see Workup, Imaging Studies, below).

The chronicity of the tear is another factor that must be considered. After approximately 6 weeks, direct repair becomes challenging, if possible at all, with native tissue. Other techniques may be necessary to establish continuity of the extensor mechanism. Regardless of the timing, repair or reconstruction is still the optimal treatment in a patient who has sustained a patellar tendon tear with subsequent patella alta and extensor mechanism dysfunction.

Relevant Anatomy

The patellar tendon is actually a ligament connecting 2 bones, the tibia and the patella. The extensor mechanism of the knee starts proximally as the quadriceps femoris muscle group. Anteriorly, the fibers of the rectus femoris tendon traverse the patella and condense inferior to the patella to insert on the tibial tubercle as the patellar tendon. The fibers of the vastus lateralis expand to the superolateral border of the patella and proximal tibia to form the lateral retinaculum. Similarly, the tendons of the vastus medialis insert into the superomedial border of the patella and tibia to form the medial retinaculum. The retinacula converge into the patellar tendon. Injuries to the tendon usually involve the adjacent retinacula as well, causing dysfunction of the entire extensor hood.

Contraindications

With disruption of the extensor mechanism of the knee, no absolute contraindications have been cited for the acute traumatic patellar tendon rupture. Perhaps in the case of an open, grossly contaminated wound, the need for a staged reconstruction following surgical debridements can be entertained. Nonetheless, the need for reestablishment of the extensor mechanism cannot be underestimated.

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