Stiffness after Knee Replacement
The knee replacement surgery is the most common non-emergent surgery performed by orthopaedic surgeons. Complications after knee replacement surgery are rare but stiff knees remain one of the common complications after knee replacement surgery.
A human knee may normally bend from 0 degrees to 135-140 degrees. About 65 degrees of movement is needed for walking, about 90 degrees for day to day activities, about 95 degrees for navigating stairs, and about 100-105 degrees for comfortably sitting and rising from a chair.
Patients are generally discharged from the hospital after they can bend their knees to about 80 to 90 degrees and are medically stable. Patients are then advised home based exercises as well as participation in physical therapy.
Stiffness after knee replacement may be graded as mild when there is inability to bend more than 90-100 degrees, moderate 70-89 or severe <70 degrees.
Similarly stiffness may be defined as inability to straighten the knee with an extension gap of 5-10 degrees or more than 20 degrees in severe cases. The knee stiffness after replacement surgery may occur due to a number of different reasons.
- History of prior surgery of the knee has been associated with higher rates of stiffness of the knee after replacement surgery. Patients who had prior unicompartmental knee replacement (UKA) or high tibial osteotomy (HTO) who now require a total knee replacement may have higher incidence of stiffness.
- Patients with decreased range of motion of the knee prior to the surgery also may experience stiffness of the knee after replacement.
- Patients with multiple medical comorbidities may experience increased incidence of stiffness post surgery.
A low threshold of pain may play a role in post knee replacement stiffness. Patients with a low pain threshold may not participate in the post replacement physical therapy.
- Implant mal-positioning is the most common intraoperative factor.
- A wrong size of implant may affect the bending and straightening of the knee leading to stiffness.
- Excessive or inadequate cutting of the bone while preparing the bone for implant placement may also lead to postoperative stiffness.
- Inadequate removal of bone spur (osteophytes) may play a role in postoperative stiffness.
- Infection of the joint may lead to swelling and inflammation that may lead to postoperative knee stiffness. The infection may also lead to formation of fibrosis tissue.
- Delayed participation in physical therapy is the most common cause of knee stiffness following replacement surgery. The delayed participation may be a result of patient selection, patient motivation, low pain threshold or a history of medical comorbidities.
- Heterotrophic ossification is formation of abnormal bone tissue in place where it is not normally present such as muscles. Formation of bone tissue in muscles may lead to postoperative stiffness.
- Excessive use of blood thinners may lead to formation of blood collections in the knee that may contribute to knee stiffness.
The range of motion of the knee continues to rapidly improve in the first 4 weeks of the surgery. The range of motion further improves in the first 3 months and continues till the first 6 months. Rarely some patients may show improvement in range of motion even after 6 months to 2 years.
Exercise therapy is started the day after surgery and the therapy in the first 4 weeks plays an important role in preventing stiffness. However patients who have inadequate range of motion despite optimal therapy may need further evaluation. Patients with limited range of motion complain of difficulty sitting and rising from the chair as well as difficulty in navigating stairs.
The physician may request radiological studies in the form of X-ray or CT after a thorough physical examination. Blood tests may be done to rule out infection of the prosthetic joint.
Nonoperative management is tried first in the form of physical therapy if the initial therapy was not optimal. Continuous passive motion machines (CPM) may help the patients achieve an optimal range of motion.
Manipulation under Anaesthesia (MUA)
Manipulation under anesthesia is a non operative technique to manage knee stiffness following surgery. The manipulation is performed in patients who are unable to bend their knees less than 90 degrees. The manipulation has best results if performed in the first 3 months of the surgery.
During manipulation, the patient is put under general anesthesia. In general anesthesia, the patient sleeps while his/her muscles are relaxed. The surgeon then tries to physically bend or straighten the knee with an aim to break the fibrosis tissue adhesions.
Not all patients are candidates for manipulation under anesthesia as excessive manipulation may carry a risk of fracture or rupture of extensor mechanism (patella fracture, patellar tendon rupture, etc).
In rare cases, where non operative methods have failed, some patients may benefit from arthroscopic lysis (cutting) of the fibrous adhesions. A small miniature camera along with miniature instruments are introduced in the knee joint and the surgeon uses the instruments to cut the fibrous adhesions.
In some cases, especially where the stiffness is a result of implant mal-position, a revision knee replacement surgery may be done.