Total hip replacement surgery is generally successful, but some individuals experience persistent pain or discomfort arising from soft tissue complications. Tendonitis, which describes the irritation or inflammation of a tendon, can develop in the tissues surrounding the newly replaced joint. This post-operative pain often occurs when the tendons are subjected to abnormal mechanical stress, either from the prosthetic components themselves or from changes in how the hip and leg function. Understanding the precise mechanisms behind this tendon irritation is important for diagnosis and effective treatment following the procedure.
Tendon Irritation Related to Implant Placement
One direct cause of tendon irritation involves a mechanical conflict between the tendon and the prosthetic hardware. This is most commonly observed with the iliopsoas tendon, a major hip flexor that runs over the front of the hip joint. The resulting condition, iliopsoas tendinopathy, typically causes pain deep in the groin area. This irritation occurs when the acetabular cup, the socket component, protrudes slightly beyond the original bone structure.
As the iliopsoas tendon slides back and forth during hip flexion, it repeatedly rubs against the exposed edge of the prosthetic cup, leading to friction and inflammation. The degree of this mechanical rubbing is influenced by the surgical placement. For example, a cup that is oversized or positioned with insufficient anteversion is more likely to create this prominent edge. Other hardware factors contributing to this friction include cement fragments or excessively long screws that may be protruding near the tendon’s path.
Biomechanical Stress and Altered Muscle Function
A significant cause of post-operative tendon pain arises from changes to the body’s walking mechanics and muscle function, independent of direct implant rubbing. Total hip arthroplasty inherently alters the geometry of the hip joint, affecting factors like leg length and the femoral offset (the horizontal distance between the center of the hip and the outer side of the thigh bone). This alteration in joint mechanics forces the surrounding muscles to operate under new loading conditions.
This mechanism primarily affects the gluteal tendons (gluteus medius and gluteus minimus), which attach to the greater trochanter. These muscles are responsible for stabilizing the pelvis when standing on one leg during activities like walking. If the femoral offset is excessively increased or decreased during surgery, it changes the leverage of these gluteal muscles, requiring them to generate more or less force to stabilize the joint. This chronic increase in workload leads to repetitive strain, fatigue, and the development of gluteal tendinopathy, often felt as pain on the lateral side of the hip.
The altered biomechanics can also manifest as an abnormal walking pattern or gait, which compounds the stress on the tendons. When the gluteal muscles struggle to stabilize the pelvis due to the new joint geometry, the entire lower limb alignment is affected. This altered movement pattern imposes chronic, excessive tension and compression on the vulnerable tendons, perpetuating the cycle of irritation and pain. Gluteal tendinopathy is a consequence of the body poorly adapting to the structural changes introduced by the new joint components.
The Role of Post-Surgical Rehabilitation and Activity Level
The patient’s actions during the recovery period represent a modifiable factor contributing to the development of tendonitis. Tendons respond to load, and improper loading during rehabilitation can cause direct injury or prevent proper healing. One common issue is an excessive or premature return to high-impact activities. Attempting to resume vigorous exercises, such as running or heavy lifting, too quickly strains the healing tendons before they have fully adapted to the new hip dynamics and restored their strength.
Conversely, insufficient physical rehabilitation can also leave the tendons vulnerable to injury. A structured physical therapy program is designed to progressively strengthen the stabilizing musculature, particularly the gluteal muscles, which are often weakened before and after surgery. Failure to diligently follow this strengthening protocol means that the hip stabilizers remain weak, leaving the tendons to absorb undue stress during normal daily movements.
Rehabilitation requires a balance: a controlled and gradual increase in the load placed on the tendons and muscles. Too little activity fails to build the necessary strength and endurance, but too much activity overloads the healing tissues. Both increase the risk of developing chronic tendon irritation. Therefore, the patient’s adherence to the prescribed activity limitations and strengthening exercises is a significant determinant in avoiding post-operative tendinopathy.