The quadriceps and patellar tendons connect the powerful thigh muscles to the kneecap and then to the shinbone, forming the extensor mechanism that straightens the knee. A complete tear of either, usually from a forceful, off-balance load or a fall, breaks that mechanism, so the knee cannot actively straighten or hold against gravity.
These are time-sensitive injuries. A complete rupture is repaired surgically, and repairing it promptly, before the tendon retracts and scars, makes the operation more straightforward and the result more reliable.
Symptoms
Common findings include:
- A sudden pop and giving way, often while loading a bent knee
- Inability to straighten the knee or keep it straight against gravity
- A palpable gap above or below the kneecap
- A kneecap that sits too high or too low, with swelling and bruising
How it is diagnosed
The exam tests the ability to actively straighten the knee, which is lost in a complete rupture. X-rays show the position of the kneecap, and ultrasound or MRI confirms whether the tear is partial or complete and which tendon is involved.
The key recognition is that a lost ability to straighten the knee after an injury is a surgical emergency of timing, even if it is not a true emergency of the hour. Dr. Lee repairs complete ruptures promptly, reattaching the tendon to the kneecap with a secure suture-anchor or transosseous construct that allows protected motion to begin.
Partial tears with an intact ability to straighten the knee can sometimes be treated without surgery, in a brace, with a careful rehabilitation program. Distinguishing complete from partial is the decision that drives everything.
Non-surgical treatment
A partial tear that preserves the ability to actively straighten the knee can be treated in a brace with a progressive rehabilitation program, monitored closely to be sure the extensor mechanism stays intact.
Surgical repair
A complete rupture is repaired by reattaching the tendon to the kneecap with a secure construct, ideally sooner rather than later, before the tendon retracts. Strong fixation is what allows protected motion to start and limits stiffness.
Recovery timeline
Recovery protects the repair while restoring motion:
- Weeks 0 to 2Brace with the knee straight to protect the repair. Begin gentle, guided motion as directed.
- Weeks 2 to 8Progressive range of motion in a brace, with weight-bearing as the repair allows.
- Months 3 to 6Strengthening and a graded return to activity and sport.
What patients commonly misunderstand
The signs not to ignore:
- Losing the ability to straighten is the red flag. If you cannot actively straighten the knee or keep it straight after an injury, the extensor mechanism may be torn, which needs prompt evaluation rather than waiting to see if it improves.
- Timing protects the result. A complete rupture repaired promptly is more straightforward than one addressed weeks later, after the tendon has retracted and scarred.
This page is general educational content authored by Dr. Lee. It is not a substitute for individual medical advice. Every patient's case is different, book a consultation to discuss yours.