Osteoarthritis of the knee is a series of symptoms and signs caused by limited, progressive destruction of articular cartilage, and is a common and frequent disease in the elderly. Advanced lesions manifest as severe joint pain, varying degrees of deformity and dysfunction, difficulty walking, and significant narrowing and loss of joint space, which seriously affects the quality of life of patients, and knee arthroplasty is the ultimate treatment for such patients.
1. Clinical data and methods
1.1 General data
There were 46 patients in this group, 25 males and 21 females. The age was 57 years – 73 years, with an average of 64 years. There were 35 cases of single knee and 11 cases of double knee. The posterior cruciate ligament type prosthesis was selected for 19 knees and the posterior stabilized type prosthesis without preservation of the posterior cruciate ligament was selected for 38 knees. All prostheses were imported, including 15 knees of Depuy prosthesis, 34 knees of Howmedica prosthesis, and 8 knees of Stryker prosthesis. Patellofemoral articular surface replacement was performed in all cases.
1.2 Indication selection
All cases in this group were patients with advanced osteoarthritis of the knee joint, meeting the following conditions: severe pain in the knee joint, varying degrees of deformity and limitation of flexion and extension activities, difficulty in daily life and walking, ineffective or unremarkable results with conservative treatment, and X-ray examination showing significant narrowing or loss of the medial tibiofemoral joint space, meeting grades 4 and 5 in the Ahlback grading method.
1.3 Surgical approach: epidural anesthesia, use of a balloon tourniquet, and a median longitudinal incision in the knee joint with the medial edge of the patella entering the joint cavity. Excision of the hyperplastic synovial tissue and the surrounding bone, excision of the anterior cruciate ligament and the medial and lateral menisci, and excision or preservation of the posterior cruciate ligament were performed. The femoral articular surface was resected using an intramedullary positioning system, and the osteotomy was performed with 5-7° of external rotation and 3° of external rotation.
The tibial articular surface is resected using an extramedullary positioning system, maintaining a 5° posterior tilt of the osteotomy surface. The patellar articular surface was resected to preserve 1 cm of bone thickness. A trial mold was placed, the medial and lateral collateral ligaments and posterior joint capsule were released and balanced, and a suitable prosthesis was selected and cemented with low-viscosity bone cement. Place the drainage tube and suture the skin.
1.4 Postoperative rehabilitation: A pain pump was installed after surgery, and continuous passive knee motion training was started immediately after returning to the ward, starting at 30° of flexion and increasing by 10° daily.
2.Results
After 6 months – 66 months of follow-up, the excellent rate was 100%.
2.1 Postoperative pain improvement evaluation.
The postoperative pain improvement was evaluated by Kuesswetter and Beumann’s evaluation criteria, which were walking pain, standing pain and quiet pain. 50 knees were free of walking pain (87%), and all 57 knees were free of standing and quiet pain (100%).
2.2 Postoperative knee motion evaluation
The mobility of the affected knee improved significantly after follow-up, and the mean mobility increased from 94°-10°-0° preoperatively to 115°-0°-0° postoperatively All flexion contractures were completely corrected, and the range of flexion improved significantly.
2.3 Comprehensive evaluation (pain, function, motion, deformity, joint stability and muscle strength).
The evaluation was based on the HSS knee score method, and the average preoperative score of this group of cases was 53.2, and the average postoperative score was 85.3, of which 45 knees had excellent results and 12 knees had good results, with an excellent rate of 100%.
3. Discussion
3.1 Principles of artificial knee joint prosthesis selection
Clinically classified according to the degree of restriction: there are two types of commonly used prostheses, namely the posterior stable type that does not retain the posterior cruciate ligament and the type that retains the posterior cruciate ligament, whether to retain the posterior cruciate ligament of the knee in artificial knee arthroplasty is still controversial, the authors believe that there are advantages and disadvantages of retaining the posterior cruciate ligament of the knee prosthesis, based on the correct grasp of the advantages and disadvantages of various types of prostheses, the operator can be based on their own experience and supporting instruments The choice is made, in general
① For younger patients, try to preserve the structurally normal posterior cruciate ligament to maximize the natural stability of the knee joint and reduce abnormal stress at the prosthesis-cement-bone tissue interface.
②For older patients or those with high degree of flexion contracture, internal and external rotation deformity, or posterior cruciate ligament lesions, a knee prosthesis that does not preserve the posterior stabilization of the posterior cruciate ligament should be selected.
③ For inexperienced operators, the choice of a non-preserved posterior cruciate ligament prosthesis often yields satisfactory results.
3.2 Excision of the diseased articular surface and placement of the prosthesis is the key to success
3.2.1 The femoral articular surface is resected with an intramedullary positioning system, with the distal cutting direction at an angle of 83°-85° to the anatomical axis of the femur, and the prosthesis is placed at a 5°-7° valgus. The anterior and posterior condylar osteotomy line is adapted to the mild external rotation of the prosthesis placement, and the femoral internal and external posterior condylar line into 3°-5°, that is, the amount of osteotomy of the internal posterior condyle is more than that of the external posterior condyle. On the premise that it does not affect the articulation relationship with the platform prosthesis, the appropriate external offset of the prosthesis can help reduce the tension of the patellar tether and the tendency of lateral patellar dislocation.
Regarding the thickness of the distal femoral osteotomy, the authors started with 9 knees operated strictly according to the instrumentation settings and found that the flexion function was unsatisfactory in some cases, and thereafter the thickness of the osteotomy was 2-4 mm more than the instrumentation settings, resulting in a significant improvement in flexion function.
3.2.2 The joint surface of the tibial plateau was resected using an extramedullary positioning system. The tibial cutting surface is perpendicular to the longitudinal axis of the tibia, i.e., more bone tissue is removed from the lateral plateau than from the medial. The tibial plateau osteotomy surface should be tilted 5° posteriorly to facilitate knee flexion. The tibial plateau prosthesis should be placed at 3°-5° of external rotation to reduce the “Q” angle and reduce the force of pulling the patella outward.
3.2.3 Replacement of the patellofemoral articular surface. Whether or not to replace the patellofemoral articular surface at the same time as total knee replacement is still under debate, but more and more scholars recently prefer to replace the patellofemoral articular surface at the same time.
The total thickness of the patella should not exceed the original thickness, otherwise, although it can increase the anterior and posterior stability of the knee joint, it is prone to subluxation or anterior knee pain, so it is better to be thin than thick, and the thickness of the residual patella should be at least 10 mm.
3.3 The importance of peripatellar soft tissue balance. Periprosthetic soft tissue balance is one of the most important steps in artificial knee arthroplasty and the most complicated surgical step, which directly affects postoperative joint function and stability. To ensure postoperative periprosthetic soft tissue balance, the principle of symmetrical knee flexion and extension gaps is mostly followed intraoperatively, which is achieved by adjusting the amount of mass resection, replacing polyethylene pads of different thicknesses, and releasing the medial and lateral pay ligaments and posterior joint capsule.
Flexion-extension gap inequality is a common problem encountered intraoperatively in two cases: the first case is more common and refers to a knee extension gap that is too narrow and smaller than the knee flexion gap.
The first case is more common and refers to a knee extension gap that is too narrow and smaller than the flexion knee gap. It occurs mostly in patients with long-term flexion knee contracture deformity or when too little bone is removed from the distal femur during surgical operation or too much is removed from the inner and outer posterior condyles, such as reducing the thickness of the polyethylene liner, which can straighten the knee, but in turn causes joint instability and dislocation in the flexion knee position. The correct method is to remove more bone from the distal femur; in the second case, the knee extension gap is wider than the knee flexion gap.
This is more common in patients with long-term extension contracture, stiffness deformity, and excessive resection of the distal femur, or too little bone from the inner and outer posterior condyles. The solution is a bone graft or pad on the distal femoral section. If flexion of the knee is limited with the addition of a thick pad, a lateral soft tissue release should be performed in the flexed knee position.