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Patellar Tendinosis

Acute Patellar Tendon Rupture and Jumper's Knee

Michael James DePalma, MD; Robert Harrison Perkins, MD


In Brief: Patellar tendinopathy (jumper's knee) may affect athletes who engage in explosive lower-limb movements. An eccentric contraction of the quadriceps when landing after a jump may lead to acute patellar tendon rupture, the end-stage of patellar tendinopathy. Plain x-rays will usually confirm the diagnosis. Treatment centers around reducing the stress placed on the patellar tendon. Postoperative functional restoration and preventive measures must address biomechanic abnormalities that may predispose patients to disruptive patellar tendon strain. As this case report shows, counseling patients who have early-stage tendinopathy on appropriate flexibility and plyometric exercises may prevent more serious damage.

Patellar tendinopathy, or jumper's knee, is a relatively common condition in patients who engage in sports that involve explosive lower-limb movements. It is characterized by localized collagen degeneration and subsequent fibrosis at the bone-tendon junction of the inferior patellar pole1-5 (figure 1).

Jumper's knee may also be viewed as a spectrum that ranges from initial overuse inflammatory changes to chronic degenerative breakdown.2 Clinically, this spectrum can be divided into four stages based on symptoms:

  • Stage 1: Pain occurs only after activity;
  • Stage 2: Pain starts at the beginning of activity, dissipates after warm-up, and recurs with fatigue;
  • Stage 3: Pain occurs at rest and with activity and affects performance; and
  • Stage 4: The patellar ligament completely ruptures.1,2

Acute patellar ligament ruptures occur more often in men than in women and usually affect athletes who are younger than 40.2,5,6 The mechanism of injury involves an eccentric contraction of the quadriceps, usually during landing after a jump.1,2 Surgical repair is successful with good functional outcome when performed within 2 weeks of injury.2,4-7 Poor outcomes have been observed in patients with postoperative patellofemoral incongruity, patella alta, or chondromalacia.2,4,6,7 This case report, involving stage 4 tendinopathy, helps illustrate predisposing factors, optimal diagnosis and treatment, and preventive interventions.

Case Report

While participating in a three-on-three basketball tournament, a 34-year-old recreational athlete "landed hard" after a lay-up. He heard an immediate "pop" and felt a cramp in his left knee. The patient was not able to bear weight or actively extend his knee.

After a courtside evaluation, he was taken to the emergency department. He reported no history of traumatic knee injuries or systemic disorders; however, during physical examination, he remembered he had been previously told by an orthopedic specialist that he had patellar "tendinitis." The condition had resolved with rest and traditional anti-inflammatory agents. The patient disclosed that he experienced intermittent anterior knee pain with squatting and ascending stairs in the month prior to his injury.

Exam. On inspection, the patella was located proximal to the tibiofemoral joint with a large effusion. The inferior patellar pole was tender, and a palpable gap in the patellar tendon was noted. The athlete could not actively extend his knee against gravity, nor could he maintain extension when his leg was passively placed in this position.

Tests and diagnosis. Plain radiographs revealed patella alta with avulsed bone fragments in the proximal portion of the patellar tendon. The distal patellar pole was elongated, possibly indicative of chronic distal patellar traction stresses, and soft-tissue shadows were consistent with induration and effusion (figure 2). The Insall-Salvati ratio (ratio of patellar tendon length to patellar height) was measured at 2.1. A normal knee is 1.0, and a variation of more than 20% indicates abnormal position of the patella. The Caton ratio (ratio between patellar articular length and the distance between inferior pole and tibial tubercle) was measured as 1.9; normal is 0.8.

Treatment. On day 6 after the injury, the patient underwent surgical repair with wire reinforcement. Both medial and lateral extensor retinacular tears were also repaired. Postoperative radiographs revealed an Insall-Salvati ratio of 1.5 and a Caton ratio of 1.2 (figure 3). Initial postoperative rehabilitation included weight bearing as tolerated, isometric knee extension, and active knee flexion to 60° at 2 weeks. At 6 weeks, the patient incorporated active knee extension into his regimen. By 3 months after surgery, he had progressed to closed-chain activities (eg, leg presses, calf raises) that addressed hip, thigh, and ankle muscle strength and flexibility. At 9 months after repair, the athlete reported mild swelling with light athletic activity, but no recurrent anterior knee pain. He returned to shooting baskets, but we do not know if he ever returned to his preinjury level of play.

The Patellar Tendinopathy Spectrum

Prior damage to the knee from overuse or trauma, biomechanic factors, and the forces inherent in landing from a jump probably contribute to tendon fatigue and patellar tendon rupture.

Tissue damage. Patellar tendinopathy has commonly been labeled "patellar tendinitis" without histologic evidence supporting this diagnosis. Histologic studies of patellar tendon specimens obtained during surgical repair have demonstrated intratendinous mucoid degeneration without the presence of inflammatory cells.2,3,5,8 However, in the acute stages, inflammatory cells may be present in the paratenon.2,8

At the advanced stage, when surgical treatment is pursued, clinically painful tendons are characterized at the cellular level by collagen fragmentation, increased ground substance, and neovascularization.2,8 This abnormal tissue may develop from the ineffectual healing response to repetitive microtears within the tendon. The natural healing process may not be capable of healing the lesion once this abnormal tissue develops.2,5,6 Therefore, it is more appropriate to diagnose "jumper's knee" as patellar tendinopathy rather than as patellar tendinitis.2,8 Treatment efforts should focus on functional restoration rather than on curtailing an inflammatory reaction.

A study by McMaster9 documented that healthy tendons do not rupture, and this construct has been widely accepted.2,6,7 Minimal differences in tensile and viscoelastic properties of the patellar tendon exist between younger and older age-groups.10 Hence, a threshold level of tendon degeneration is probably requisite to tendon rupture.7

In the athlete older than 35, less intense repetitive microtrauma can induce age-related pathologic changes,6 perhaps because of less efficient vascular and reparative properties.7 Although conclusive evidence is lacking, otherwise healthy patellar tendons probably rupture as a consequence of repetitive-microtrauma-induced degeneration. More important, it has not been proven whether structural changes of tendinopathy or a decreased resistance to fatigue is integral to injury. Regardless, this moment of tendon failure represents end-stage (stage 4) jumper's knee.

The athlete in this case report did not undergo histologic examination. Within the 6 months before his injury, an orthopedic specialist had diagnosed him with patellar "tendinitis," and he was symptomatic with activities of daily living (stage 2).

Biomechanic factors. Several static and dynamic biomechanic factors that increase tensile load on the patellar tendon have been related to patellar tendinopathy.2 However, few studies have identified the causal relationships between these factors and the incidence of patellar tendinopathy.

Anatomic characteristics that may be associated with patellar tendinopathy include patella alta, poor patellofemoral tracking, patellar instability, malalignment, and leg-length discrepancy.2,11 Distal and proximal abnormalities, such as pes planus, decreased ankle dorsiflexion, coxa vara, and femoral anteversion, contribute as well.2,8

Forces generated in landing are substantially greater than those generated during jumping. Approximately 60% of the landing force is absorbed distal to the knee.8 A wide range of hip or knee flexion combined with forefoot landing can further reduce landing forces by another 25%. Inflexibility or weakness of the gluteal, quadriceps, hamstrings, tensor fascia lata, or calf musculature can restrict range of motion and increase loads experienced by the anterior knee.8,12 Rapid midfoot pronation on dynamic testing allowed more force transmission to the knee.8

When surgical intervention occurs within 2 weeks after a complete rupture, good functional outcome typified by less knee pain, minimal lower limb muscle atrophy with less than 20% loss of strength, and return to baseline activity have been achieved.2,5,13 The presence of pre- and postoperative patella alta or baja, chondromalacia, or patellofemoral incongruity can predispose the patient to recurrent anterior knee pain and adversely affect functional outcome.6,13 A high-riding patella (confirmed by an increased Insall-Salvati or Caton ratio) will decrease the moment arm of the knee extensor mechanism, increasing tensile loads placed on the patellar ligament.6 Furthermore, patella alta may initiate chondromalacia, leading to patellofemoral pain.6 Biomechanic abnormalities that increase tensile load on the patellar tendon have been related to patellar tendinopathy, but the causal contribution of these findings is still uncertain.

Studies, such as the one by Witvrouw et al,14 have documented the positive correlation between clinical overloading of the patellar tendon and the development of jumper's knee. However, strong prospective evidence is lacking regarding the relationship of intrinsic factors and patellar tendinopathy.

Flexibility. Retrospective and cohort studies support the concept of a relative lack of flexibility leading to tendon strain and subsequent tendon overload injury.11,14 Witvrouw et al14 prospectively studied the incidence of patellar tendinopathy in student-athletes 17 to 21 years old and found that decreased flexibility of the quadriceps and hamstring muscles predisposed the subjects to patellar tendinitis. The authors suggested that routine evaluation for inflexibility and properly restoring flexibility when identified is crucial to preventing patellar tendinitis.

Our literature search failed to discover a randomized, prospective study assessing the effect of such stretching efforts on the incidence of patellar tendinitis. A 1984 epidemiologic study15 of the occurrence of jumper's knee in volleyball players did not find a significant difference in the incidence of patellar tendinopathy between players who used plyometric training (ie, jumping after landing from jumps of various heights) and those who did not. The authors concluded that plyometric training, three times per week, was less harmful to tendons than once believed.


A conditioning program incorporating routine trunk and lower-limb stretching, as well as plyometric training, may help diminish excessive stress on the patient's anterior knee. Further research is warranted to delineate the relationship between conditioning and anterior knee stress and the specific training parameters necessary to minimize strain on the tendon. However, it is intuitive that repetitive landing with one or more predisposing biomechanic factors brings the tendon to the fatigue threshold more quickly. Thus, the entire kinetic chain must be addressed when physicians approach functional restoration of jumping athletes.


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Dr DePalma is chief resident and Dr Perkins is a clinical assistant professor in the department of physical medicine and rehabilitation at The Ohio State University in Columbus, Ohio. Address correspondence to Michael J. DePalma, MD, Dodd Hall, The Ohio State University, 480 West Ninth Ave, Columbus, OH 43210; e-mail to [email protected].

Disclosure information: Drs DePalma and Perkins disclose no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.