➢ Conceptually, so-called limited arthroplasty techniques for the treatment of osteoarthritis of the knee are an attractive future alternative for selected patient populations.
➢ It is important to manage patient expectations and to educate patients with informed preoperative discussion of the available options, including early focal resurfacing and delayed total arthroplasty.
➢ Important intraoperative considerations include ensuring adequate implant defect coverage, recessing implant components just below the articular surface, careful mapping of the defect to ensure appropriate curvature of the implant, and confirming uniform cement coverage.
➢ Tibiofemoral alignment should be corrected before or at the same time as placement of limited arthroplasty devices such as inlay components.
➢ Limited arthroplasty techniques are currently being employed in orthopaedics, with encouraging short-term results; however, additional long-term results are necessary before definitive recommendation for or against their use can be made.
Cartilage lesions are among the most commonly reported knee injuries1 and can progress to osteoarthritis2-4. These lesions have been reported to cause limitations in quality of life similar to severe osteoarthritis4. A number of biological treatment approaches have been proposed, and these approaches can be classified into one of five categories: palliative, reparative, restorative, reconstructive, and corrective. Debridement is a palliative measure aimed at stabilizing the lesion and eliminating mechanical symptoms. Marrow stimulation, such as microfracture or chondroplasty, is an example of a reparative technique. In contrast, chondral and osteochondral transplantation aim to restore injured tissue. Allografts and prosthetic devices are used to reconstruct defects, and osteotomy is used to address the underlying anatomy of the disease. With the exception of palliative treatment and reconstruction involving the use of a prosthetic device, all of these approaches require prolonged rehabilitation to ensure adequate biological response, remodeling, and healing.
While excellent long-term results have been reported5-8, conventional arthroplasty has been associated with limitations as onlay surface replacements introduce a non-native joint surface geometry, complicating pain relief and functional results and potentially threatening implant survival. This is especially true for both younger, more active patients and for heavy, morbidly obese patients. Inferior clinical outcomes and higher revision rates have been reported in both groups7-10.
Knee resurfacing platforms are a response to the challenge of joint preservation, allowing the surgeon to employ a thin, contoured, metal implant that is sized to the lesion and specific to the patient’s joint surface following intraoperative mapping—the potential first step in arthroplasty under the continuum of care for joint arthrosis and arthritis (Fig. 1). Currently, forty-seven different metallic sizes and shapes for the knee and a corresponding set of nineteen polyethylene component choices are offered commercially. All-metallic components are made of a cobalt-chromium (CoCr) alloy and have titanium (Ti) coverage where they interface with bone (e.g., at the site of screw fixation and at the undersurface of the articular component); ultra-high molecular weight polyethylene (UHMWPE) components are cemented into the prepared implant bed.
Both basic science11-15 and clinical16-19 studies have offered potential support for so-called limited arthroplasty, particularly for the treatment of chondral and osteochondral defects in a carefully selected population. Rather than a completely new treatment option, inlay resurfacing should be seen as an extension of current reconstructive methods, with its own specific technical demands (Table I).
Monopolar Focal Femoral Condyle Inlay Resurfacing
This treatment concept has been approved in international markets and currently remains under Food and Drug Administration-Investigational Device Exemption (FDA-IDE) investigation in the United States. Localized treatment of full-thickness chondral and osteochondral lesions with focal femoral condyle prosthetic resurfacing expands the range of treatment options available prior to arthroplasty. Successor procedures such as unicondylar or total knee replacement provide a sound clinical exit strategy when larger surface reconstruction is warranted.
In general, this interim treatment solution is recommended for patients between the ages of forty and sixty years as well as for older, more active patients with otherwise healthy knees14,15. This option is designed to protect the remaining normal cartilage while providing a biomechanically stable and congruent fill of the defect11-13.
A small parapatellar incision is made directly over the medial or lateral weight-bearing defect. The surgeon establishes a perpendicular working access to the joint surface with use of a drill guide and pin and drives a cannulated step drill into the bone until the proximal shoulder of the drill is flush to the articulating surface. Under visual controls, the fixation component is placed at the correct height and the patient-specific joint surface curvature is measured intraoperatively during a condylar resurfacing procedure involving the HemiCAP system (Arthrosurface, Franklin, Massachusetts) (Fig. 2). The implant socket is prepared with a corresponding surface reamer, and a sizing trial allows for proper assessment of the cartilage-implant interface. The final articular component is inserted into the taper of the fixation component after being aligned on the implant holder. Progressive tapping on the impactor engages articular and fixation components, which are joined with a Morse taper interlock. Final placement of the surface prosthesis is targeted slightly recessed (1.0 mm) to the surrounding articular cartilage to account for nearby cartilage thickness variations during weight-bearing, thereby avoiding any overloading or deleterious effects to the opposing side (Fig. 3).
Kirker-Head et al. described the biocompatibility of the monopolar focal femoral condylar inlay in the caprine model11. They found a continuous trabecular and subchondral bone interface surrounding the screw and the resurfacing component. Cartilage flow from the adjacent native tissue was observed, covering the implant-cartilage interface. Their data implied the safety, biocompatibility, and functionality of the implant, and the authors stated that expanded animal or preclinical human studies were justified on the basis of their research. Several clinical studies of the HemiCAP Focal Femoral Condyle Resurfacing Prosthesis (Arthrosurface) have been undertaken to date, with follow-up of up to six years12,15,19.
Von Hasselbach and Witzel reported on 121 patients (mean age, 52.5 years) who were managed with the HemiCAP Resurfacing Prosthesis20. At the time of short-term follow-up (mean, fourteen months), nearly normal Hospital for Special Surgery (HSS) Knee Scores were achieved (mean, 95.3 of 100). No deleterious cartilage effects on opposing articular surfaces were observed during second-look arthroscopic evaluations, which were performed for non-device-related indications. No periprosthetic radiolucency or implant subsidence was found on radiographic follow-up.
The results of a prospective U.S. Food and Drug Administration (FDA) phase-II multicenter feasibility trial are pending. Thirty-six of forty patients were followed for two years. The average age of the patients was forty-seven years. Two subjects were lost to follow-up, one died before the two-year end point, and one underwent conversion to a unicondylar knee replacement. At baseline, patients showed substantial pain and functional deficiencies on the basis of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score. The WOMAC is a widely used, proprietary set of standardized questionnaires used by health professionals to evaluate the condition of patients with osteoarthritis of the knee and hip. The WOMAC measures five items for pain, two for stiffness, and seventeen for functional limitation. For each item, the possible range of scores is 0 to 100. Items are summed for each subscale, resulting in possible ranges of 0 to 500 for pain, 0 to 200 for stiffness, and 0 to 1700 for physical function. Most commonly, a total WOMAC score is created by summing the items for all three subscales. In the phase-II feasibility trial mentioned above, the average pain score improved postoperatively from 308 to 68 of 500 and the function score improved from 999 to 223 of 1700. Remarkable improvement was seen by three months after the procedure, with the pain score reduced to 68 of 500 and the function score reduced to 246 of 1700. Further improvement was seen across all domains from one to two years postoperatively, with the final mean total WOMAC score improving from 1436 to 341 of 2400.
Bollars et al.17 reported excellent results at a mean of 35.3 months of follow-up in a study of eighteen patients with a mean age of fifty-one years who had been managed with the study device. Normal or nearly normal International Knee Documentation Committee (IKDC) Subjective Knee Form scores were reported for fifteen (83%) of the eighteen patients. The Knee injury and Osteoarthritis Outcome Scores (KOOS) were compared with normative age-matched scores and showed a close match across all domains. These excellent results for pain and function were seen in middle-aged, well-selected patients with full-thickness cartilage and osteochondral defects. The authors concluded that “Patient profiling and assessment of confounding factors, in particular mechanical joint alignment; meniscal function; and healthy opposing cartilage surfaces, are important for an individual treatment approach and successful outcomes.”
To our knowledge, the longest-term study of patients managed with focal resurfacing was reported by Becher et al.16. Twenty-one patients with a mean age of fifty-four years were followed for a minimum of five years (range, five to six years). Radiographic joint space preservation and significant improvements in all KOOS subdomains, the Tegner activity level, and Short Form-36 scores were observed. The authors concluded that focal resurfacing was an excellent option for the treatment of “large full-thickness cartilage and osteochondral lesions of the knee in middle-aged patients.”16
Bipolar Tibiofemoral Inlay Resurfacing
Bipolar knee inlay resurfacing was introduced in 2008. The intent of this procedure is to provide an option for patients with early tibiofemoral arthrosis (Fig. 4). The implant is marketed as minimally invasive, preserves the menisci and cruciate ligaments, and retains the osseous architecture of the knee joint. As with focal monopolar femoral condyle implants, these larger bipolar tibiofemoral implants come in a number of different surface convexities to allow for precise and contoured inlay resurfacing. As the tibiofemoral alignment cannot be changed with inlay implants, the mechanical tibiofemoral axis has to be taken into consideration during surgical planning (Fig. 1).
In our experience, the ideal candidates for this procedure have been middle-aged patients who have redeveloped substantial pain and limitations in function and activities of daily living after the failure of previous nonoperative or operative intervention and who require additional treatment of monocompartmental arthrosis. Preoperative clinical examination should show a stable knee with <5° of mechanical malalignment, a range of motion with a deficit of <10° of flexion or <5° extension, satisfactory meniscal function, and a body mass index (BMI) of <30 kg/m2. Patients who are affected by factors outside these parameters (for example, slight malalignment or ligamentous instability) and who are being considered for resurfacing should have these issues corrected prior to or in conjunction with the bipolar knee inlay resurfacing. A compounding effect needs to be considered if more than one of these factors is present. Contraindications to the procedure include metabolic disorders affecting implant fixation, osseous deformation, mechanical malalignment affecting the ipsilateral compartment, a BMI of ≥30, and widespread degeneration that cannot be covered by the prosthesis. Careful patient selection needs to be carried out on an individual basis (Fig. 1) while taking patient expectations and activity demands into account.
The patient is positioned and prepared for standard knee arthroscopy in a manner allowing for deep knee flexion during femoral preparation. The medial compartment is visualized through an anterolateral portal (Fig. 5-A), and a full-length anteromedial skin incision is placed vertically 1 cm medial to the patellar tendon, extending proximally from the middle pole of the patella down to 1 cm distal to the joint line. It is important to maintain capsular integrity by limiting the capsulotomy to the anteromedial portal for the arthroscopic tibial preparation. Extending the skin incision distally below the joint line facilitates exposure, thereby avoiding posterior pin deviation and skin interference during reaming of the posterior femoral implant bed. Any concomitant findings are addressed before attention is directed toward the tibial defect.
Arthroscopic Tibial Resurfacing
Access to the tibial plateau can become challenging as normal knee kinematics include a tibial rollback phenomenon during knee flexion. Therefore, arthroscopically assisted tibial preparation facilitates visualization and work flow. The knee is placed in 20° to 30° of flexion with valgus stress as the tibial templates are trialed until the underside curvature matches the plateau surface with full contact in all planes. An osseous rim of >5 mm is maintained around the implant in order to avoid placement of the tibial component too far anteriorly or posteriorly.
The tibial drill guide is attached and is aligned front to back with the tibial plateau. A small incision is placed over the anteromedial aspect of the proximal part of the tibia, the tibial template is kept parallel to the tibial plateau, and a drill pin is placed through the center of the tibial template defining the axis of the tibial tunnel. To avoid pin deviation, great care must be taken to maintain proper axial alignment without excessive torque. The tibial pilot drill is advanced over the drill pin into the center of the tibial defect. The introducer, driver, and blade stop are assembled and are advanced into the prepared tunnel until the tip of the introducer is flush with the tibial plateau. The blade stop is set at the appropriate depth for reaming of the bone for placement of the implant. A blade drive shaft is moved through the tunnel and is connected to the tibial cutting blade, which is introduced through the anteromedial portal.
Initial counterclockwise rotation with a high-speed drill ensures an even cutting engagement into the plateau. Once the cutting blade reaches the proximal end of the blade stop through clockwise rotation, preparation of the tibial implant bed is complete. The appropriate sizing trial verifies a congruent, slightly recessed fit of the tibial component while the tibial cutter remains in place. If adjustments are needed, the blade stop is turned clockwise with a wrench to lower the implant margins. A 90° turn lowers the blade stop and implant floor by 1 mm after repeat reaming. Before the final tibial implant is cemented into its implant bed, preparation and implantation of the femoral component is performed.
The femoral drill guide is placed over the defect (Fig. 5-B) with four points of contact to establish a perpendicular working axis to the joint surface. Femoral resurfacing is then carried out in a manner similar to the monopolar femoral condylar resurfacing technique described previously. Three overlapping surface reams, controlled by the established working axis, are used to prepare a 2-mm-deep bone bed. Cement is applied to the underside of the femoral articular component and is impacted, engaging the Morse taper between the components (Fig. 5-C).
Miniaci et al. reported on a prospective series of thirty-eight patients with a mean age of forty-eight years and a mean duration of follow-up of nineteen months (range, twelve to twenty-seven months) at the 2011 meeting of the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS)21. The study demonstrated significant improvement in the KOOS subcomponent scores for pain, symptoms, activities, and sports (p < 0.0001) (Fig. 6). The average visual analog scale (VAS) pain score was reduced from 6.9 to 2.7 at the time of the latest follow-up. Within the first six weeks postoperatively, range of motion had returned to normal in 89% of the patients. Radiographically, no loosening or mechanical failure, implant subsidence, prosthetic disengagement, or periprosthetic cyst formation was observed.
Focal Bipolar Patellofemoral Inlay Resurfacing
The patellofemoral joint is characterized by a complex joint surface geometry and high transarticular forces. Symptomatic patellofemoral lesions therefore need to undergo careful examination to establish the underlying cause and to determine the best course of treatment. The HemiCAP Focal Patellofemoral Resurfacing Prosthesis (Arthrosurface) (Fig. 7-A) was introduced in 2006 and provides an extension of reconstructive procedures for focal bipolar lesions. Patients should demonstrate normal knee kinematics, or concomitant procedures should be performed to reestablish proper tracking of the patellofemoral joint.
Intraoperatively, patellar and trochlear components are matched to the native geometry14, which allows for a congruent surface reconstruction in patients with focal traumatic or degenerative disease and failed previous biological procedures. A detailed description of the operative technique has been published previously14,19.
Provencher et al.14 evaluated the patellofemoral kinematics of eight fresh-frozen cadaveric knee specimens following inlay resurfacing of the trochlea with use of a real-time pressure sensor pad (Tekscan, Boston, Massachusetts). Each specimen was tested in three different conditions (intact, defect, and inlay resurfacing) and was assessed for patellofemoral contact area, peak contact pressure, and peak contact force. Peak contact force increased from 13 to 18 N and peak contact pressure increased from 23 to 31 kg/cm2 in the defect state, in which edge-loading and peak contact forces were highest at the periphery of the lesion. Resurfacing restored peak contact force and pressure to 88% and 90% when compared with the intact state. Contact area was restored to 85% of normal. The study supported the importance of congruent defect reconstruction in the patellofemoral joint with anatomic reapproximation of the patellofemoral surface and knee contact pressures. Clinical series are currently undergoing the peer-review process to validate the procedure at the two to seven-year follow-up time point.
HemiCAP Wave Resurfacing Arthroplasty
Patellofemoral arthroplasty has been performed for more than thirty years. Until recently, all implants were derived from total knee arthroplasty designs and were implanted as an onlay into the patellofemoral joint. The introduction of FDA-approved inlay resurfacing has changed arthroplasty from requiring deep, sizable bone cuts to allowing superficial surface reams for an axis-controlled, bone and tissue- preserving surface reconstruction. Pain relief, postoperative recovery, and functional improvement all may be influenced by the maintenance of joint height and soft-tissue tension. The goal therefore remains to avoid overstuffing of the patellofemoral joint and to reestablish normal patellofemoral tracking in a smooth and congruent central compartment. The HemiCAP Wave resurfacing prosthesis (Arthrosurface) provides a thin, anatomical implant with a lateral flange that avoids overstuffing by means of congruent inlay implantation with curvatures measured specifically for each patient (Fig. 7-B).
The patient is placed with the knee in extension, and the offset drill guide is used to establish a perpendicular working axis to the central trochlear surface. Surface mapping and measurement of superior-inferior and medial-lateral offsets is performed. A central reamer is advanced until the outer edge mark is flush with the medial and lateral facets. A guide block is chosen according to previous surface measurements and is secured in the trochlear groove. A set of guide block reamers is used to prepare the implant bed. Congruent inlay fit to the surrounding articular surface is tested with a sizing trial. A pilot hole for insertion of the tapered screw fixation is prepared, and the femoral resurfacing component is aligned on the implant holder and is inserted into the prepared socket. The fixation and articular components are connected with use of the impactor, and the prosthesis is firmly seated in the trochlea (Fig. 7-C).
An alignment guide allows for testing of the targeted patellar component placement while range of motion is observed. The drill guide is placed over the marked location on the patella, and a guide pin is inserted to establish a normal working axis. A centering shaft is placed over the guide pin and is secured in the patella. The contact probe provides patellar offset measurements, and a corresponding surface reamer is used to prepare the implant bed. A sizing trial reconfirms a congruent fit along the transition from implant to native cartilage. Two different contour configurations can be trialed to ensure optimum tracking. Cement application onto the implant rather than into the socket is preferred as it ensures even cement distribution surrounding the patellar component. The final patellar component is aligned and is cemented into the implant bed.
While the technique has gained increasing acceptance among knee surgeons for the treatment of patellofemoral disease, ongoing studies continue to evaluate the clinical benefits and durability of the procedure.
While total knee arthroplasty remains an excellent choice for patients with end-stage arthritis of the knee, less-invasive procedures are increasingly gaining acceptance. Most notably, unicompartmental knee arthroplasty has rapidly increased in popularity, growing 32.5% from 1998 to 2005, whereas total knee arthroplasty increased only 9.4% over the same period22. There remains a great potential for further growth as unicompartmental knee arthroplasty accounts for only 8% of all knee arthroplasty procedures. However, unicompartmental knee arthroplasty may have a more limited future among younger patients, for whom the revision rate is reportedly double that of total knee arthroplasty4,23,24. One study of patients who underwent unicompartmental knee arthroplasty demonstrated that the implant survival rate increased markedly with the age of the patient; specifically, the seven-year survival rate was 76% for patients younger than sixty years old, compared with 86% for patients sixty-one to sixty-nine years old and 91.3% for patients more than seventy years old. Clearly, patients younger than sixty-five years old who maintain an active lifestyle may benefit from a less-invasive procedure while maintaining unicompartmental knee arthroplasty or total knee arthroplasty as a potential last resort.
The transition from biologic treatment strategies to joint resurfacing offers biomechanical and clinical advantages because of the availability of custom-fitting implants specific to the size of the defect and the contour of the native surface geometry. However, full defect coverage has to be ensured to adequately address specific lesions. Most notably, important considerations for normal knee kinematics such as the menisci, cruciate ligaments, and the native joint contour are preserved. Also, soft-tissue tension is unaltered as transarticular pressure profiles are normalized, eliminating overstuffing and potentially improving functional outcomes and relieving pain12-14. Healthy articular surfaces are preserved and share weight-bearing with the implant, potentially improving long-term survival. The new contoured prosthetic surface is secured within the bone bed, and a high-pitched screw fixation anchors the implant, theoretically reducing the risk of lesion propagation through the offloading effect at the defect perimeter.
Basic science studies have so far confirmed the validity of this design and treatment approach. Histological data11 obtained one year after implantation have confirmed device biocompatibility and incorporation into the femoral condyle. Becher et al. evaluated transarticular tibiofemoral pressure profiles in a variety of settings and reported that the device is biomechanically safe12,13,15. A study of patellofemoral kinematics after limited trochlear resurfacing demonstrated that the prosthesis provides a favorable alternative to prior implant designs by reestablishing anatomic patellofemoral surface and knee contact pressures14.
Established biological procedures for focal cartilage repair have been expanded through new approaches involving smaller knee implants and patient-specific prosthetic inlays. The combination of new techniques and implants allows us to simultaneously address pathology and preserve healthy tissue, offering a joint-preservation strategy that is consistent with the goals of early intervention. Two to five-year clinical results support limited arthroplasty techniques such as HemiCAP resurfacing as a potentially viable option. However, while basic science studies have offered encouraging results, larger patient series and longer-term results will be required to establish performance criteria and related outcomes. These recommendations for care are summarized in Table II.
Source of Funding: The primary author (M.J.G.) received no external funding for this study. The senior author (A.M.) receives consulting, royalty, and stock benefits from Arthrosurface.
Investigation performed at the Cleveland Clinic, Garfield Heights, and Performance Orthopaedics and Sports Medicine, Clinton Memorial Hospital, Wilmington, Ohio
Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2013 by The Journal of Bone and Joint Surgery, Incorporated