This article is more than 5 years old. Information may no longer be current.
UniSpacer most suited for younger patient
Douglas W. Jackson, MD, interviews Richard H. Hallock, MD, of Orthopedic Institute of Pennsylvania.
---Richard H. Hallock,
MD chief executive officer, Orthopedic Institute of Pennsylvania
Douglas Jackson, MD: What are your indications for the use of the UniSpacer?
Richard H. Hallock, MD: The most important factor for obtaining a good result with any arthroplasty procedure, especially with the UniSpacer Knee System [Centerpulse], is patient selection. The decision should consider not only the clinical symptoms and radiographic finding but also the treatment history, functional limitations, patient demographics and patient expectations.
Implantation of the UniSpacer is intended to delay total knee arthroplasty [TKR] and is therefore ideally suited for younger patients who have the most to gain from anatomy preservation. The 35- to 55-year-old patients are concerned with immediate pain relief and also the condition of their knees over a 30- to 50-year period.
In these patients, the indication for the use of the UniSpacer is the treatment of isolated medial compartment degenerative joint disease. Most of my patients have a minimal amount of degeneration in the lateral and patellafemoral compartments. Patients must also have intact or reconstructed ligament structures to ensure stability. Our focus continues to be further defining the ideal candidate for the device.
Jackson: Is the device suitable for older patients and for obese patients?
Hallock: Our initial experience suggests that the UniSpacer does not provide any significant advantage over traditional treatment options in older patients. I typically use a traditional UKR in patients over 65 years of age.
Our initial data also suggest that obesity does not have a detrimental effect on Knee Society or Lysholm scores. Two distinct patient groups have achieved equivalent assessment scores — one with an average BMI of 27 and the other having an average BMI of 38. We can provide an average of 80% reduction of pain, so patient and surgeon expectations must be set appropriately.
The UniSpacer can provide very satisfying relief to a patient with disabling knee pain. My patients have tried NSAIDS and injections of either cortisone or viscosupplementation, and most patients have had at least one arthroscopic debridement over the years prior to their UniSpacer surgery. Most patients have some mild residual symptoms postoperatively, which is why I would never offer this procedure prophylactically to a patient with only mild or recreational symptoms.
The best UniSpacer candidates are patients who would be considered osteotomy candidates, if not for a variety of considerations that make osteotomy a less than ideal solution from either the surgeon’s perspective or the patient’s perspective. These considerations include surgical morbidity, postoperative valgus alignment and obesity.
Jackson: What are the contraindications?
Hallock: There are some absolute contraindications. Patients older than 65 do not have much to gain from a bridge procedure. I will offer those patients a low-friction arthroplasty. On physical examination, any patient with a fixed flexion contracture greater than 5º will never regain full extension post-operatively. This will exacerbate any pre-existing patellafemoral disease that will lead to anterior knee pain. If I have doubts, I will have them do preoperative stretching exercises or physical therapy to see if the contracture is correctable.
Patients should have minimal lateral compartment and patellofemoral compartment degeneration. Lateral compartment degeneration must be carefully scrutinized since implantation of the UniSpacer changes the mechanical axis of the knee and shifts more of the joint loads back to the lateral compartment. As a result, an asymptomatic lateral compartment with significant degeneration may become symptomatic or suffer from rapid progression of the degeneration after implantation of the UniSpacer.
The extent of the degeneration in all compartments should be evaluated preoperatively utilizing AP erect, lateral, tunnel and skyline radiographs. The AP erect view must demonstrate medial joint space narrowing and varus axis deviation. Medial femoral subluxation is usually associated with bone loss on medial aspect of the medial tibial plateau. This bone loss creates a dome-shaped medial tibial plateau that can make the UniSpacer implant unstable and is therefore a contraindication.
|
The lateral view x-ray is important for evaluating long-standing ligament instability. Both ACL and PCL insufficiency are contraindications for implantation of the UniSpacer. The UniSpacer acts as a self-centering bearing that moves across the surface of the tibia in tandem with the femur. Excessive AP translations resulting from ACL or PCL deficiency can cause instability of the UniSpacer implant and discomfort for the patient. The MRI is also a useful tool in evaluating the integrity of the ACL/PCL in cases where the history and clinical exam are questionable.
Jackson: How do you distinguish PF pain from medial compartment pain?
Hallock: It is occasionally difficult to distinguish symptoms of medial disease from PF disease. The skyline radiograph is helpful for confirming patellofemoral disease with the presence of osteophytes along the border of the PF joint, subluxation of the patella or joint space narrowing, especially in the lateral facet of the PF joint.
Surgeons must distinguish between medial compartment symptoms and patella femoral symptoms to avoid the problem of patients with significant, unexpected postop patella femoral pain. I rely on clinical correlation of the radiology with patient history and physical examination to avoid the pitfalls of patient selection.
Jackson: What about osteochondral lesions and osteonecrosis?
Hallock: I will use an MRI to rule out large areas of AVN of the medial femoral condyle. Central lesions on the femur or tibia that will be spanned by the UniSpacer may still be suitable for this implant; however, lesions that create a defect on the anterior or posterior aspect of the femoral condyle will not allow proper implant translation during flexion and extension. This can lead to a potential dislocation of the implant.
Jackson: What are the key technical points to remember?
Hallock: My goal at the time of surgery is to correct the varus deformity with an internal shim. The UniSpacer is a mobile-bearing device with no fixation to the femur or tibia. Reproducible motion is mandatory prior to wound closure.
Creating this motion requires sculpting of the remaining femoral condyle and tibial plateau until they match the surfaces of the implant as closely as possible.
Implantation of the UniSpacer Knee System begins with an arthroscopic evaluation of the patella femoral joint, lateral compartment and ACL/PCL complex. Once proper indications are confirmed, the leading edge of the medial meniscus is resected back to a stable rim. I try to limit the arthroscopic portion of the technique to 10 to 15 minutes because most of the work is best performed through the arthrotomy.
Exposure of the medial compartment is obtained through a 2- to -3-inch medial parapatellar incision. Once the medical compartment is exposed, I remove osteophytes from the medial edge of the medial femoral condyle and tibial plateau to allow the MCL to regain its normal excursion. This creates the medial joint space that will be occupied by the UniSpacer.
The postop alignment of the knee is dictated by space available in the medical compartment instead of being arbitrarily set to a specific value through the operative technique. A reciprocating rasp is an effective tool for removing irregularities in the femoral and tibial articular surfaces. The goal is to shape the femoral condyle and tibial plateau to conform with the surfaces of the UniSpacer. A more conforming surface will promote a quicker recovery and fewer postop effusions.
I pay special attention to one particular region on the femoral condyle: the area just anterior to the femoral notch created by the convergence of the two femoral condyles toward the femoral sulcus. Cartilage just above the notch must be removed to allow the anterior lateral flange of the device to nest into this region during full extension. Failure to relieve this area of impingement will create pain in full extension and actually prevent the device from tracking normally during extension of the knee.
Fluoroscopy is required to confirm proper sizing and tracking of the implant. The mini C-arm fluoroscopes provide an adequate field of view and are less cumbersome in the OR.
Both AP and ML fluoroscopic views are important for evaluating the fit. A properly sized device provides full anterior-to-posterior coverage of the medial tibial plateau in a true lateral fluoroscopy view. It is critical to ensure that the UniSpacer follows the femoral condyle as it translates posteriorly across the tibial with flexion.
The radius of femoral surface must be open enough to avoid gouging into the femoral condyle in extension. I am never bashful about trying several trial devices to ensure that I have good stability, adequate conformity with the femur and smooth, repeatable motions of the device.
Jackson: What are the limitations for patients postop?
Hallock: The biggest limitation of the UniSpacer, as with any arthroplasty, is limitation of postoperative activities. Patients cannot expect to resume high-impact activities such as running and jumping. Low-impact activities such as golf, biking, and walking are all satisfactory. Although high-impact activity will not damage the device, it can cause pain and/or effusion in what still is an arthritic knee.
Improper patient selection will lead to unnecessary failures. It is very easy for the patient and the surgeon to be seduced into “trying” a less-invasive procedure based on the premise that there is “nothing to lose.” Unfortunately there is always a potential to lose something. This list includes generic surgical complications such as infection or deep vein thrombosis, or the only specific complication for this procedure — dislocation of the device. The indications are clear and should be strictly adhered to.
Surgical technique is also critical. All surgeons must be adequately trained and updated as the technique evolves. The technique requires attention to detail and perseverance to attain proper implant motion. Anything less than that will lead to a prolonged recovery and/or a clinical failure or complication. This procedure can take more time to complete than a routine TKA, and the surgeon must be willing to spend that time.
A final limitation includes postoperative management. Management does not just include wound management, physical therapy and x-ray evaluation. These patients will require continued encouragement, similar to an osteotomy, because the recovery can be prolonged. Both the patient and the surgeon must demonstrate patience to allow enough time to maximize the recovery process. Since the operation does “burn any bridges,” there might be a temptation to convert the UniSpacer to a next-step procedure prematurely during the recovery period. Some patients may take up to one full year to gain maximum benefit.
Jackson: What are realistic expectations for most patients?
Hallock: Most of my patients achieve between 80% to 100% pain relief and this pain relief can sometimes take three to six months to achieve. The first implantation was done in May of 2000, so my longest follow-up at this point is 38 months. I tell patients preoperatively that this particular device is relatively new, but the concept of interpositional arthroplasty predates TKRs. Metallic tibial hemiarthroplasty implants have a long track record in orthopedic implant history that predates the early versions of the total condylar knee replacement. The McKeever and the MacIntosh are the two most widely know versions of these devices. The results for these devices in patients with RA were marginal. The results in patients with OA, however, were significantly better.
I explain that I don’t have 10-year data on the UniSpacer. I educate patients on preservation of anatomy vs. pain relief, so that they understand the long-term staging of procedures that may be necessary for their younger knee.
As a bridge procedure in younger patients, we expect that nearly all patients will go on to a next-step procedure, but they will do that at an older age with complete preservation of bony and ligamentous anatomy.
For more information:
- Potter TA, Weinfeld MS, Thomas WH: Arthroplasty of the knee in rheumatoid arthritis and osteoarthritis. J Bone Joint Surg. 1972;54A:1-24.
- Scott RD, Joyce MJ, Ewald FC, Thomas WH: McKeever metallic hemiarthroplasty of the knee in unicompartmental degenerative arthritis. J Bone Joint Surg. 1985; 67A:203-207.
- Emerson RH, Potter TA: The use of McKeever metallic hemiarthroplasty for unicompartmental arthritis. J Bone Joint Surg. 1985;67A:208-212.