Minimally invasive unicompartmental knee replacement: rationale and correct indications

The Valgus Stress Radiograph Does Not Determine the Full Extent of Correction of Deformity Prior to Medial Unicompartmental Knee Arthroplasty

Routine preoperative stress radiographs have been advocated, in part, to determine "full correctability" of deformities before proceeding with unicompartmental knee arthroplasty (UKA) despite limited data supporting their utility. Fifty consecutive patients undergoing medial UKA with robotic navigation were studied. In 20° of flexion, significantly greater correctability was achieved after removal of osteophytes by an additional 1.8°, with a mean corrected alignment of 2.5° varus. Seventy-four percent of knees were not correctable to neutral alignment or more. In conclusion, preoperative stress radiographs have overstated value in patients undergoing medial UKA since the full extent of correctability of varus deformity cannot be determined until after removal of osteophytes and since most deformities are not fully correctable to neutral in UKA.

A Cohort Study Predicts Better Functional Outcomes and Equivalent Patient Satisfaction Following UKR Compared with TKR

BACKGROUND

Total knee replacement (TKR) is considered the gold standard treatment for advanced osteoarthritis of the knee (Choong and Dowsey, Int J Rheum Dis 14:167-74, 2011; Satku, Singapore Med J 44:554-556, 2003). Unicompartmental disease can be treated with unicompartmental knee replacement (UKR) or TKR. Some surgeons prefer the proven track record of TKR, while others prefer the more normal joint kinematics, enhanced proprioception and range of movement achieved with UKR (Hopper and Leach, Knee Surg Sports Traumatol Arthrosc 16:973-9, 2008; Satku, Singapore Med J 44:554-556, 2003). However, there is reported low satisfaction amongst younger patients undergoing UKR (Robertson et al., Acta Orthop Scand 71:262-7, 2000).

QUESTIONS/PURPOSES

The purpose of this study is to compare patient-reported outcomes, satisfaction and perception of knee normality in age-matched groups of postoperative TKR and UKR patients aiming to answer the following question: Does UKR have lower patient satisfaction than TKR in younger patients?

METHODS

Sixty-eight patients were recruited from the care of a single surgeon. Patients with isolated medial compartment osteoarthritis, stable ACL and less than grade 3 lateral patellar disease underwent UKR. All other patients underwent TKR. Patients were assessed with validated knee scores. Satisfaction was assessed with a visual analogue scale.

RESULTS

There was no statistical difference in patient satisfaction or perception of knee normality scores between the two groups, despite better functional scores including WOMAC, SF-36 and Oxford knee in the UKR group.

CONCLUSION

Patient satisfaction is similar amongst TKR and UKR patients despite better functional outcome in terms of recreation and sport with UKR. This may reflect higher preoperative expectations in patients undergoing UKR. Further work is needed to assess this.

Retrospective analysis of total knee arthroplasty cases for visual, histological, and clinical eligibility of unicompartmental knee arthroplasties

We retrospectively analyzed 97 total knee arthroplasty cases with medial osteoarthritis from seven participating surgeons in our teaching hospital to determine the percentage of patients who met the following eligibility criteria for unicompartmental knee arthroplasty (UKA): healthy cartilage in the lateral compartment based on (1) visual analysis, (2) histological analysis and (3) absence of UKA contraindications based on clinical analysis. The cases with healthy lateral cartilage, intact anterior cruciate ligament and posterior cruciate ligament, lack of patello-femoral arthritis, preoperative range of motion (ROM) greater than 90, and genu varum less than 10° represented 21% of the 97 cases studied. This percentage would likely have been higher had the cases been assessed earlier in the disease process. It was concluded that there is the potential to utilize UKA more frequently in the future.

Mobile or fixed unicompartmental knee prostheses? In-vitro wear assessments to solve this dilemma

The unicompartmental knee prosthesis is an attractive alternative to total knee arthroplasty. Current UKP devices can be subdivided into two groups based on different design principles: fixed bearing knees, where the ultra-high molecular weight polyethylene meniscal component snap or press fits into the tibial tray, and mobile bearing designs which facilitate movement of the insert relative to the tray. The present study was aimed at comparing the in-vitro wear behaviour of fixed and mobile unicompartmental knee menisci under two configurations: the femoral components were cemented into a custom-made metallic block or, as a novelty of the present study, into a synthetic femur (i.e. under conditions which should better reproduce the in-vivo behaviour). Analyses were performed using a displacement-control knee wear simulator with "three-plus-one" stations. All the kinematics tests were set in accordance with the ISO 14243-1,2,3. Fixed and mobile polyethylene menisci showed a different wear behaviour: the fixation-frame influenced directional load transfer through each component in a qualitative and quantitative way. In fact, gravimetric results showed that under the metal block holder fixation, mobile components worn more than fixed components (weight losses of 8.7±2.0 mg and 2.6±1.09 mg, respectively); on the other hand, under the synthetic femur configuration, differences in wear behaviour were less pronounced and mobile menisci underwent a slightly lower weight loss than fixed components (4.5±2.2 mg vs. 6.7±1.4 mg). This different trend was explained in relation to the kinematic schemes of the two fixation methods. Raman spectroscopy, used to evaluate the UHMWPE crystallinity changes induced by mechanical stress, showed that mobile menisci specimens were more affected than the fixed components in both their superior and inferior surfaces, independent of the fixation-frame. In conclusion, if tested under conditions which should better reproduce the in-vivo behaviour, mobile UKPs did not show a worse wear behaviour than fixed components in terms of weight losses, although UHMWPE changes at the molecular scale could be detrimental.

Can the method of fixation influence the wear behaviour of ZrN coated unicompartmental mobile knee prostheses?

BACKGROUND

Modern unicompartmental knee prostheses represent a valid alternative to total knee replacement. It is known that variations in clinical alignment lead to altered biomechanics and abnormal wear. The aim of this study was to assess the influence, on wear behaviour, of two different cementing interfaces of the femoral components tested on a knee joint wear simulator.

METHODS

The wear tests were run in a knee wear simulator at a frequency of 1.1 Hz for 3 million cycles in accordance with ISO 14243-3. Twelve commercial mobile GUR 1020 UHMWPE meniscus specimens articulated in between 12 cobalt-chromium-molybdenum alloy femoral and tibial components covered by a multi-layer of chromium nitride and a final layer of zirconium nitride ceramic coating to prevent ion release from the substrate. Two wear tests were performed: in the first test, each femoral component was cemented into a custom made metallic-block shaped to perfectly host it. In the second test, synthetic composite femurs received the femoral components on the basis of guidelines used in current surgery.

FINDINGS

The two cementing interfaces showed a significantly different wear behaviour, quantified as mean weight loss (P<0.001). Scanning electron microscope examinations of new and tested metallic components showed macro- and micro-pores of few microns on both configurations.

INTERPRETATION

The wear pattern observed at 3 million cycles showed differences between the two methods of fixation for the meniscus femoral components.

Strategies for articular cartilage lesion repair and functional restoration

Injury of articular cartilage due to trauma or pathological conditions is the major cause of disability worldwide, especially in North America. The increasing number of patients suffering from joint-related conditions leads to a concomitant increase in the economic burden. In this review article, we focus on strategies to repair and replace knee joint cartilage, since knee-associated disabilities are more prevalent than any other joint. Because of inadequacies associated with widely used approaches, the orthopedic community has an increasing tendency to develop biological strategies, which include transplantation of autologous (i.e., mosaicplasty) or allogeneic osteochondral grafts, autologous chondrocytes (autologous chondrocyte transplantation), or tissue-engineered cartilage substitutes. Tissue-engineered cartilage constructs represent a highly promising treatment option for knee injury as they mimic the biomechanical environment of the native cartilage and have superior integration capabilities. Currently, a wide range of tissue-engineering-based strategies are established and investigated clinically as an alternative to the routinely used techniques (i.e., knee replacement and autologous chondrocyte transplantation). Tissue-engineering-based strategies include implantation of autologous chondrocytes in combination with collagen I, collagen I/III (matrix-induced autologous chondrocyte implantation), HYAFF 11 (Hyalograft C), and fibrin glue (Tissucol) or implantation of minced cartilage in combination with copolymers of polyglycolic acid along with polycaprolactone (cartilage autograft implantation system), and fibrin glue (DeNovo NT graft). Tissue-engineered cartilage replacements show better clinical outcomes in the short term, and with advances that have been made in orthopedics they can be introduced arthroscopically in a minimally invasive fashion. Thus, the future is bright for this innovative approach to restore function.

Unicompartmental knee arthroplasty: a review of literature

There has been a resurgence of interest in unicompartmental knee arthroplasty (UKA) for treatment of medial unicompartmental knee osteoarthritis (OA). Improved prosthetic design, minimally invasive surgical techniques, and strict patient selection criteria have resulted in improved survivorship and functional outcomes. A review of orthopedic literature was conducted regarding the advantages of UKA versus total knee arthroplasty (TKA), UKA indications, survivorship, conversion of UKA to TKA, rehabilitation, and outcomes. The UKA appears to be a viable option for patients with knee medial compartment OA, including younger and active patients. Survivorship rates of 94% to 97% at 10 years have been reported.

Development of a patient-specific femoral component for unicompartmental knee replacement

This study describes the development of a novel, patient-specific unicompartmental knee prosthesis. The geometries of the lateral and medial condyles are approximated by polynomials, instead of single radius circles that are commonly used. Furthermore, a database containing the geometries of healthy knees is used to generate appropriate knee geometries according to certain measurements of the unhealthy knee. This new method enables a customized design of a unicompartmental knee replacement that will closely resemble the articulating surfaces of the normal, healthy knee joint.

Minimally Invasive Surgical Technique in Total Knee Arthroplasty: A Learning Curve

Clinical experience of learning a new technique of minimally surgery for total knee arthroplasty is presented. Close monitoring of the technique, pitfalls, learning tips, and tricks are discussed. A “learning phase” is identified as approximately 10 months or 21 knee replacements using minimally invasive technique. It took 50 operations before the surgical time equaled the open technique. There was no incidence of increased complications during the learning phase. Functional results such as stair climbing, walking distance, and walking with aids was significantly better after minimally invasive technique than after standard technique.

[Minimally invasive implantation in unicondylar arthroplasty]

Knee arthroplasty has become one of the most successful standard procedures in orthopaedic surgery. With a more frequent use in young and active patients bone-saving procedures have become more important. The goal is to save good bone stock for the revision procedure. Therefore, unicompartmental knee arthroplasty is a good example. Instrumentation and minimally invasive surgical techniques have been improved so very good long-term results and early functional results are achieved. The paper describes the surgical technique with true capsule incision and extramedullary alignment technique. In a prospective study, the early functional results with the ZUK implant were excellent. The implant may not be indicated for every knee situation and an exact differential indication and sound surgical technique are necessary. Its use, however, in cases with unicompartmental knee arthritis, contributes to excellent early rehabilitation and to maintaining autologous bone. Therefore, the minimally invasive unicompartmental knee arthroplasty is a sensible alternative to other options.

Retrieval of an impacted trial implant during unicompartmental knee arthroplasty

We report a case of impacted trial implant during Oxford unicompartmental knee arthroplasty. We have successfully used AO-ASIF (Association for the Study of Internal Fixation) principles to retrieve the implant without any damage to the metallic implant and adjacent bone and joint.

Clinical experience using a minimally invasive surgical approach for total knee arthroplasty: early results of a prospective randomized study compared to a standard approach

There has been recent attention concerning minimally invasive techniques for knee arthroplasty. It is not clear whether these complicated techniques can be reproduced across multiple centers and for all surgeons. This prospective, randomized, multicenter study was carried out to assess safety and efficacy of a minimally invasive total knee arthroplasty. The study consisted of 80 knees. There were no differences in blood loss, operative time for completion of surgery, infection, and ultimate wound healing. There were 4 knees with delayed wound healing in the minimally invasive surgical technique group versus 1 in the standard group, which did not affect outcome. Early clinical and radiographic results were also indistinguishable. At 12 weeks follow-up, there was no difference in mean Knee Society objective and functional scores. In summary, in this study, minimal incision total knee arthroplasty demonstrated no improvement over a standard approach.

Minimally invasive revision total knee arthroplasty

Exposure in revision total knee arthroplasty can be difficult. For example, eversion of the patella may require a number of procedures including vastus snips, V-Y turndowns, and tibial tubercle osteotomies. A minimally invasive approach further adds to exposure difficulties. We report a new approach for exposure during difficult revision total knee arthroplasties. A soft tissue envelope technique allows retraction of the patella and avoids eversion. This technique reduces the size of the incision, reduces quadriceps muscle damage, and enhances exposure. It is essential that appropriate instrumentation is used along with down sized femoral and tibial cutting blocks. We report all 17 revision knee arthroplasties using this technique including unicompartmental revisions, tibial component revisions, and femoral component revisions. Followup averaged 29 months (range, 24-39 months). We had one case of posterior retained cement after a full revision with no subsequent complications. One patient required an arthroscopic lateral release for patellar maltracking. Preliminary results are encouraging using improved instrumentation we find essential for enhanced exposure. We believe this a reasonable approach for selected total knee arthroplasty revisions.

LEVEL OF EVIDENCE

Therapeutic study, level IV (retrospective case series). See the Guidelines for Authors for a complete description of levels of evidence.

[Is computer navigation a useful tool in unicompartmental knee arthroplasty? A pilot cadaver study]

We conducted this pilot cadaver study to investigate whether the use of a navigation system during minimally invasive unicompartmental knee arthroplasty leads to more consistent results than the conventional hand-guided technique. We describe the accuracy of implant positioning in using standard instrumentation and computer navigation. Radiographic assessment showed that accurate component placement was achieved using both methods. These results were not statistically significant. The computer navigated femoral component placement without intramedullary (IM) rod was as accurate as the conventional method with IM rod. The study showed that computer navigation can produce accurate results even without an intramedullary rod. Image guidance can maintain the accuracy of the standard instrumentation and enhance 3D vision and the intraoperative orientation of the surgeon.

Minimally invasive navigated knee surgery: an American perspective

Minimally invasive total knee replacement surgery may make it possible for patients to undergo the procedure with less pain and recover from the surgery more quickly than has been previously possible. However, minimally invasive techniques have the potential for being associated with a number of complications, including implant and limb malalignment. Computer-assisted technologies used in conjunction with minimally invasive techniques allow the accuracy with which the procedures are performed to be retained.