Description of Snapping Hamstrings

Snapping hamstrings are a rare condition, but they can cause significant disability in patients who have this pathology.

Lateral, or biceps, snapping hamstrings are usually due to a presumed genetic or injured state where the direct arms of the long and short heads of the biceps no longer attach to the posterolateral aspect of the fibular styloid. In these patients, when they perform a deep squat, the biceps femoris tendon can roll over the fibular head when one squats down. Upon arising, the tendon will often “snap” back into position. This can be a quite debilitating problem in patients who present with these symptoms. In addition, these patients commonly have irritation of the common peroneal nerve because it is adjacent nature to the snapping biceps tendon. Patients often have paresthesias and “zingers” going down into the lateral aspect of their leg and the dorsum of the foot due to the irritation of the common peroneal nerve.

Symptoms of snapping hamstring:

  • Deep pain within knee when squatting down
  • Audible or visible “clunk” when arising after squatting
  • Numbness or tingling over the outside of the knee with activities

While the causes differ between medial and lateral snapping hamstrings, the presenting symptoms are often similar.

Snapping medial hamstrings often present with similar findings. The “clunk” that one endures with going down into a deep squat and arising can be quite dramatic and it can sometimes appear like the joint is subluxing. Just like with lateral biceps tendon snapping, the occurrence of this varies between patients, with some having a dramatic snap in all circumstances and others having it only occasionally. We have noted that about half of our patients have had this onset with no particular injury, while the other half often have it after a hamstring-based ACL reconstruction, medial meniscus repair, or other type of surgery over the medial aspect of the knee which can cause scar tissue. The snapping is believed to be due to catching of the semitendinosus and/or gracilis tendons when they cross the semimembranosus tendon. However, dynamic ultrasound studies so far have not been able to elucidate which of these tendons it may be, or if both tendons cause the snap, between patients.

On physical exam, these patients will often have pain on palpation of the biceps tendon attachment on the fibular styloid. In addition, performing a deep squat will often reproduce their symptoms. We have found that in the most severe cases, the biceps femoris will snap in all circumstances, while in others it will only occasionally snap and catch.

The physical exam almost always involves having the patient perform a deep squat to replicate their symptoms. In some circumstances, a patient can replicate their medial knee snapping symptoms by putting full weight on their involved side and trying to hyperextend their knee. In this instance, the snapping may occur directly over the posteromedial knee. The examiner must place one’s fingers directly over the hamstring tendons to verify that this is a source of where the snapping occurs. In almost all circumstances, one can localize the snapping to the hamstrings within 5 to 6 cm of the posteromedial joint line.

We recommend that a thin slice MRI, to include the posterolateral knee structures, be obtained in these patients to verify that the biceps femoris attachment on the posterolateral aspect of the fibular styloid is not normal. X-rays should also be obtained to make sure there is not an osteochondroma or other pathology that could be confused with this condition.

Plain x-rays may be useful to determine if there is an osteochondroma or a bone spur (osteophyte) causing the snapping hamstrings. We have not found the use of MRIs to be particularly useful in diagnosing medial snapping hamstrings, but they remain useful to verify that there is no other pathology in this area of the knee which could be confused with this diagnosis (posterior horn meniscal tears, large Baker’s cysts, and other causes).

Are you experiencing snapping hamstring symptoms?

There are two ways to initiate a consultation with Dr. LaPrade:

You can provide current X-rays and/or MRIs for a clinical case review with Dr. LaPrade.

You can schedule an office consultation with Dr. LaPrade.

(Please keep reading below for more information on this condition.)

Treatment for Snapping Hamstring

The treatment of medial snapping hamstrings involves eliminating the cause of the snapping. Unfortunately, this is such a rare condition that a definitive treatment course has not been determined. In some patients, it has been found that simply releasing the gracilis and semitendinosus tendons at their attachment along the pes anserine bursa, followed by scar tissue release of the tendons proximally, is very successful at relieving the snapping symptoms. In others, a surgical excision of the snapping hamstring tendon(s) with an open hamstring harvester has also been performed. However, even in the best of circumstances, recurrent snapping can occasionally occur because it is becoming increasingly recognized that the hamstring tendons can regenerate, with studies demonstrating on ultrasound that they can regenerate as soon as 6 weeks to 3 months after their excision (these studies were performed for ACL reconstruction hamstring harvest evaluation). Thus, the results of a surgical release, or harvesting, of the medial hamstring tendons does always not prove to be as successful as the treatment of lateral snapping hamstrings. Thus, ongoing studies are still being performed to determine the ideal treatment for this rare condition.

The treatment for snapping biceps femoris tendons is to reattach the biceps femoris back to the fibular styloid. This usually involves the use of suture anchors.


For lateral snapping biceps repairs, patients are kept on crutches for 6 weeks to make sure that the soft tissue heals and then they slowly increase their activities. It usually takes 4 to 5 months to return back to full activities after this repair. Patients who have a medial snapping hamstring release or excision are often allowed to increase their activities as tolerated over the course of 6-8 weeks after surgery.

Related Studies

Snapping Hamstrings Injury FAQ

Both the inside (medial) and outside (lateral) aspect of the knee can have catching and snapping of the hamstring tendons. The causes are different depending upon which portion of the knee is involved, but the symptoms can be similar. Usually, the patient will squat down and the hamstrings will slip on each other and there can be often an audible or visible catch that is described as snapping hamstrings.

1. What is causing a snapping lateral hamstring?

A snapping lateral (outside of the knee) hamstring tendon is usually due to the biceps femoris tendon  not being attached to the top of the fibular styloid and only being attached to the outside or lateral aspect of the fibula. What happens with a lateral snapping hamstring is that the lack of attachment of the biceps tendon on the posterolateral aspect of the fibular styloid can cause the biceps tendon  to slide back and forth over the fibular styloid with deep knee flexion. This can often result in an audible or visible slipping of the tissue. With time, the repeated snapping of the biceps tendon can cause some irritation of the common peroneal nerve which  has been noted to result in both sensory and motor deficits in some patients.

2. What causes snapping medial hamstrings?

Snapping medial hamstrings usually occur because one of the pes anserine tendons, either the gracilis or semitendinosus, will get caught in scar tissue and in the course of deep flexion or extension of the knee, and the tendons will slip over each other and often have an audible snap back into place. Snapping medial hamstrings can occur after meniscus repairs, after ACL surgeries, after trauma, and sometimes occur spontaneously with no known trauma.

3. What type of sounds do snapping hamstrings make?

The sounds that snapping hamstrings make can be quite audible and dramatic.   It can occur as a loud clunk, especially on the medial side, or as a barely audible snap on the outside of the knee. They usually occur with deep knee flexion, but snapping medial hamstrings can also catch in knee extension or hyperextension.

4. What is the surgical treatment for snapping hamstrings?

The surgical treatment for a lateral snapping hamstring is to repair the biceps femoris back to the posterolateral aspect of the fibular styloid. This is usually done by cleaning off the scar tissue on the bone about this area and placing suture anchors and then placing the direct arms of the long and short heads of the biceps back to the fibular styloid. It is important to do this when the knee is out straight so the suture anchors can be placed with the knee in flexion, but they should be tied with the knee out straight so there is not extra tension which could lead to the anchors pulling out or having the sutures pull out of the tissues over time.

The usual treatment for medial hamstrings snapping is to remove the offending tendon that is snapping. This is similar to how a hamstring would be harvested for an ACL or other ligament surgery at the knee. Sometimes, the tendons can be released at their attachment on the tibia at the pes anserine region.  However, simply removing scar tissue around the snapping hamstrings often results in a recurrence of the snapping.

Learn How We Can Help You Stay Active