Key Treatment Strategies for Patellar Tendinopathy of the Knee

Jumper’s knee is patellar tendinopathy of the knee caused by repetitive jumping or landing. The tendon is repeatedly stretched, which produces micro-damage to the tendon tissue and triggers an inflammatory response that leads to the pathology. The tendon is made up mostly of densely packed parallel collagen fibers (about 86%), mainly type I collagen, with other components including elastin (2%), proteoglycans (1-5%), and inorganic components (0.2%). The patellar tendon has reduced vascularity in its proximal and distal regions, which is also related to the tendinopathy that follows.

Looking at the stress on the patellar tendon during 0 to 90 degrees of knee flexion and during slow and fast level walking, one study found that during flexion the central proximal posterior region showed the highest peak stress and strain, followed by the central distal posterior, central distal anterior, and central proximal anterior regions. The stress changes during slow and fast walking followed a similar trend, corresponding to the common sites of patellar tendinopathy.

Epidemiology

Patellar tendinopathy

• Sports that require excessive jumping or running, such as volleyball, basketball, soccer, and running
• Prevalence of 40-50% among high-level volleyball players and 35-40% among basketball players
• One of the three most common causes of knee pain in recreational runners
• Similar rates in men and women
• The term tendinopathy may be more appropriate than tendinitis, because pathological tissue findings show poor tendon healing and degeneration due to insufficient recovery

Patellar tendon rupture

• More common in men around 40 years old
• Usually occurs with quadriceps contraction while the knee is flexed at about 60 degrees
• Ruptures are usually complete and commonly occur at the bone-tendon junction

Quadriceps tendon rupture

• More common at 60 to 70 years old, with a male-to-female ratio of about 4 to 8:1
• About twice as likely in the dominant leg, and about 12% of people have it in both legs
• Approximately 1 to 2 cm above the upper edge of the patella
• Under age 40 it tears in the mid-portion of the tendon; over 40 it tears at the tendon-bone junction

Risk factors

• Positively correlated with training volume and training intensity
• Poorer flexibility, including of the hamstrings and quadriceps, increases risk
• Higher body weight
• Past history of trauma
• Also worth noting are patellar alignment and tracking problems, including patella alta, patella baja, and patellar malalignment/maltracking
• Possibly related conditions: ankylosing spondylitis, rheumatoid arthritis, systemic lupus erythematosus (SLE), other autoimmune diseases, diabetes, chronic kidney disease, gout, or a past history of knee surgery
• A small number of cases are related to antibiotics: use of fluoroquinolone antibiotics within the past 90 days

History

• Anterior knee pain that worsens with exercise or prolonged knee flexion
• Increased load activities, such as going down stairs or downhill activity
• Participation in sports with excessive acceleration, deceleration, and jumping
• Gradually worsening anterior knee pain (Blazina classification)
  • Stage 1: pain after activity
  • Stage 2: pain during and after activity, but performance is not affected
  • Stage 3: pain during and after activity that affects performance

Physical examination

• Local tenderness: local tenderness at the patellar tendon attachment, the mid-portion of the quadriceps tendon, or the quadriceps tendon attachment
• Pain: pain worsens when extending or flexing the knee against resistance
• Reduced range: poor flexibility of the quadriceps and hamstrings

Diagnostic tools

Diagnosis can be made mainly through clinical assessment and does not always require routine imaging, but imaging can help rule out other conditions.

X-ray

• Allows side-to-side comparison, taken from different angles including AP, lateral, tunnel, and patellar (sunrise or merchant) views
• Rules out avulsion fracture, patellar subluxation, Sinding-Larsen-Johansson syndrome, Osgood-Schlatter disease, and other conditions

Ultrasound

• Accuracy 83%, sensitivity 87%, and specificity 82%
• Shows thickening and a larger cross-sectional area; on average, the normal patellar tendon is about 3-6 mm thick and 10-15 mm wide
• Chronic tears show abnormal echogenicity or hypoechoic areas

MRI

• Accuracy 70%, specificity 82%, but lower sensitivity at 57%

Basic management

Tendinopathy

• Mainly conservative: rest, and in the acute phase oral NSAIDs or local medication injection may be considered (avoid corticosteroids)
• Modality treatment to reduce pain and chronic inflammation
• A patellar compression strap or taping has a short-term effect
• Isometric exercise reduces pain better than aerobic and resistance exercise

Complete tendon rupture

• Surgery is recommended, usually within two weeks; beyond six weeks, complications are more likely and the prognosis is worse

Non-surgical advanced treatments

• Platelet-rich plasma injection (PRP)
• Prolotherapy
• Tendon scraping or hydrodissection
• Ultrasonic tenotomy
• Extracorporeal shockwave therapy (ESWT)

There has been a good deal of research on this area in recent years, mostly with positive effects. A suitable treatment can be chosen based on the physician’s clinical experience, the severity of the condition, and the patient’s acceptance. As an initial intervention I most often start with dextrose prolotherapy (DPT) or shockwave therapy. Treatment recommendations for partial tears are similar to those for tendinopathy, but if improvement is limited, more aggressive treatment can be considered.

Non-surgical exercise training

• Correcting faulty posture (including everyday posture, training movements, and sport-specific technique)

• Rehabilitation exercise and strength training

• The most common eccentric training is a slow decline squat on a 25-degree slope board, three sets of 15 repetitions, twice a day, for 12 weeks

• One study found that heavy, slow, concentric and eccentric resistance exercise (squat, leg press, and hack squat) was associated with better tendon improvement and subjective functional gains than eccentric exercise alone (progressing each week, starting at 15 repetition maximum (RM) in week 1, then 12RM in weeks 2 and 3, 10RM in weeks 4 and 5, 8RM in weeks 6 to 8, and finally reaching 6RM in weeks 9 to 12)

• With similar progressive-loading training, designed as an appropriate program for the individual situation, the training in this BJSM study was associated with an additional benefit of a trend toward a higher return-to-sport rate (43% vs 27%), noticeably less pain during exercise (VAS 2 vs 4), and better patient satisfaction in the progressive-loading group. These are trial results and do not predict any individual’s outcome.

• Overall, return-to-sport training can be divided into the stages below. Most of what is described above falls mainly in the second stage, which bridges the first and third stages so that return to sport can go smoothly. In the past, some patients had markedly improved pain symptoms after treatment but did not show clear changes on ultrasound imaging; other assessments can serve as a way to monitor ongoing training, for example the countermovement jump (CMJ). One study found a certain correlation between tendon structure and lower-limb function or quadriceps muscle performance in patients with patellar tendinopathy, and tracking changes in these data can help address this issue.

Surgery

Surgical intervention is considered only after 3 to 6 months of the above treatment without clear improvement.

Postoperative rehabilitation

Strict immobilization for 4 to 6 weeks, then beginning concentric and eccentric training, with a goal of returning to sport in 4 to 6 months.

• Weeks 0 to 3: active flexion of 0 to 45 degrees and passive extension
• Weeks 4 to 6: progress to active flexion of 0 to 90 degrees and passive extension
• After week 6: straight-leg raises
• After week 8: stationary bike and water running
• After 3 months: progressive quadriceps training
• After 4 months: jogging
• After 6 months: preparing to return to sport

Possible complications

• Inability to flex the knee
• Reduced knee extension strength
• Postoperative infection
• Knee degeneration

References

• J Athl Train. 2022 Jul 1;57(7):621-631. doi: 10.4085/1062-6050-0049.21. Clinical Management of Patellar Tendinopathy
• Int J Numer Method Biomed Eng. 2020 Sep;36(9):e3379. doi: 10.1002/cnm.3379. Epub 2020 Jul 25. A biomechanical analysis of 3D stress and strain patterns in patellar tendon during knee flexion
• J Orthop Res. 2022 Oct;40(10):2320-2329. doi: 10.1002/jor.25262. Epub 2022 Jan 17. Relationships between tendon structure and clinical impairments in patients with patellar tendinopathy
• Br J Sports Med. 2021 May;55(9):501-509. doi: 10.1136/bjsports-2020-103403. Epub 2020 Nov 20. Effectiveness of progressive tendon-loading exercise therapy in patients with patellar tendinopathy: a randomised clinical trial