Impact of patellar tendinopathy on isokinetic knee strength and jumps in professional basketball players

Key points

1. 01Quadriceps limb symmetry index at 60 deg/s was significantly lower in players with patellar tendinopathy (81% vs 91%, p=0.001)
2. 02A 'camel's back' isokinetic curve was present in 58% of affected legs vs 7% of healthy legs (specificity 93%)
3. 03Single-leg countermovement jump and one-leg hop test results were not significantly different between groups
4. 04Hamstring strength and hamstring-to-quadriceps ratios were not associated with patellar tendinopathy
5. 05VISA-P score and quadriceps LSI at 60 deg/s together predicted patellar tendinopathy with 72.6% accuracy

How it was conducted

Design

Cross-sectional observational study with preseason screening across three consecutive seasons (2017-2020)

Participants

62 male professional basketball players (Pro A, Pro B, National 1 levels); mean age 25.0 +/- 4.0 years, mean weight 96.0 +/- 11.0 kg

Groups

24 players with unilateral patellar tendinopathy vs 38 players without knee pain

Knee strength assessment

Isokinetic dynamometer (Humac) at 60 deg/s and 180 deg/s concentric; limb symmetry index calculated

Jump assessments

Single-leg countermovement jump (Abalakov belt) and one-leg hop test (tape measure)

Primary outcome

Comparison of isokinetic quadriceps and hamstring strength and jump performance between groups

What they found

• Quadriceps LSI at 60 deg/s: PT group 81 +/- 11% vs control 91 +/- 8% (p=0.001)
• Quadriceps LSI at 180 deg/s: PT group 87 +/- 10% vs control 92 +/- 6% (p=0.01)
• Hamstring LSI at 60 deg/s: PT group 91 +/- 6% vs control 89 +/- 7% (p=0.31, not significant)
• Countermovement jump LSI: PT group 86 +/- 10% vs control 90 +/- 6% (p=0.08, not significant)
• Hop LSI: PT group 96 +/- 3% vs control 94 +/- 5% (p=0.13, not significant)
• Relative quadriceps strength at 60 deg/s: PT legs 2.14 +/- 0.42 Nm/Kg vs non-PT legs 2.54 +/- 0.44 Nm/Kg (p=0.0001)
• H/Q ratio at 60 deg/s: PT legs 74 +/- 14 vs non-PT legs 64 +/- 12 (p=0.0001)
• Absolute CMJ: PT legs 42.7 +/- 6.3 cm vs non-PT legs 41.2 +/- 7 cm (p=0.19, not significant)
• Camel's back curve: 58% of PT legs vs 7% of non-PT legs (p=0.0001; sensitivity 58.3%, specificity 93%)
• Predictive model for player-level PT: QLSI60 OR 0.01 (95%CI: 0.001-0.06, p=0.006) + VISA-P OR 0.94 (95%CI: 0.90-0.99, p=0.03); ROC area for QLSI60 = 0.813 (95%CI: 0.694-0.931), cut-off 89% giving sensitivity 78.9% and specificity 79.2%
• VISA-P score: PT group 81 +/- 16 vs control 94 +/- 10 (p=0.002)

Limitations

• Patellar tendinopathy was diagnosed clinically without ultrasound or MRI confirmation of tendon structure
• Only male professional basketball players were included, limiting generalizability to female athletes, other sports, or bilateral tendinopathy cases
• Cross-sectional design prevents causal inference about whether strength deficits precede or follow tendinopathy onset
• Strength testing was concentric only and may not reflect eccentric demands relevant to jump-landing tasks

Why it matters

For patients

Basketball players with patellar tendon pain can expect their jumping ability to be largely preserved, but laboratory-based quadriceps strength testing may reveal deficits not detectable by functional tests alone.

For clinicians

Preseason isokinetic screening using a quadriceps LSI cut-off of 89% at 60 deg/s combined with the VISA-P score (cut-off 94 points) can identify players with patellar tendinopathy; the presence of a camel's back isokinetic curve adds further diagnostic specificity.

For readers

Jump tests alone are insufficient to detect patellar tendinopathy in athletes who are still able to train and compete; isokinetic dynamometry is the more sensitive screening tool for this condition.