Survivorship of unicondylar knee replacement (UKR) exceeds 85% at 10 years. During long term follow-up, progressive osteoarthritis (OA) and loosening are typical of UKR failure. The decision to revise UKR is complex as radiographic findings are not always consistent with clinical symptoms. This study of revised UKR compares intraoperative assessment of component fixation and progressive OA with prerevision radiographic evaluations.

Twenty-seven UKR were retrieved from 22 female and 5 male patients. Patient age and time in situ averaged 76 (68–87) years and 79 (25–156) months, respectively. At index arthroplasty, all knees received a fixed-bearing medial UKR with cement fixation. Prior to revision, radiolucent lines and component alignment were assessed on radiographs according to Knee Society guidelines. Suspected revision reasons based on clinical and radiographic evaluation included aseptic loosening (63%), progressive OA (22%), and wear (15%). During revision surgery, component fixation was manually assessed and graded as well-fixed or loose, and progressive OA was graded using Outerbridge classification. Intraoperative and radiographic assessments were completed independently.

Average Knee Society Scores declined > 30 points to 53+18 (pain) and 43+11 (function) before revision. During revision surgery, femoral and tibial component fixation were graded as loose in 19 (70%) and 9 (33%) knees, respectively. There was Grade III or IV progressive OA in the lateral or patellofemoral compartment of 15 (56%) and 16 (59%) knees, respectively. Radiolucent lines were evident in 8 of 19 loose femoral components and 5 of 9 loose tibial components. In contrast, 3 of 8 well-fixed femoral components and 6 of 18 well-fixed tibial components had radiolucent lines. There were 11 loose femoral components and 4 loose tibial components without radiolucent lines. Radiographic limb alignment averaged 3°+3° valgus immediately after index UKR. Change in limb alignment ranged from 0° to 17° at revision. Tibial or femoral component alignment changed 5° to 9° in 12 (44%) knees and > 10° in 5 (19%) knees. Eight of these 17 knees (47%) had malaligned components graded as loose.

The prevalence of progressive OA at revision UKR was more than double occurrence suspected from radiographs. Interpreting radiographic indications for loosening was difficult. Radiolucent lines predicted loosening in 46% (13/28) of the components graded as loose and falsely predicted loosening in 35% (9/26) of the components graded as well-fixed. Radiolucent lines were absent in 15/28 (54%) of the loose components and changes in component alignment > 5° were associated with component loosening in < 50% of the knees. Rigorous attention to clinical symptoms and careful interpretation of radiographic phenomena are needed to determine indications for revision in UKR patients.

There is renewed interest in unicondylar knee replacements (UKR) to meet the increasing demand for less invasive surgical procedures for knee arthroplasty. UKR survivorship exceeds 85% at 10 years, with unconstrained (round-on-flat) designs showing significantly better survivorship than conforming designs. However, round-on-flat articulation shave the potential for poor wear performance and more conforming, mobile-bearing UKR designs have been advocated. The purpose of this study was to evaluate the wear performance of unconstrained UKR polyethylene bearings retrieved at revision knee arthroplasty.

Forty-two UKR (eight designs) were retrieved from 26 female and 16 male patients. Patient age averaged 73+10 (45–89) years and time in-situ averaged 7+4 (1–19) years. Revision reasons included loosening (45%), progressive osteoarthritis (17%), polyethylene wear (14%), instability (5%), and other (19%). Retrospective radiographic review of radiolucent lines and component alignment was completed. Polyethylene damage (severity score, 0–3) and location were measured using optical microscopy and digital image analysis.

81% of the polyethylene inserts had a concave deformation located on the central or posterior third of the articular surface, consistent with damage due to femoral component articulation. Abrasive damage on 29 (69%) inserts was consistent with impingement between the polyethylene and extra-articular cement or bone. There was delamination in the central region of 7 (17%) inserts and on the extreme posterior rim of 3 (7%) inserts. Severity score averaged 2.0+1.2 for abrasion and 0.5+1.0 for delamination. Radiographic component position was correlated with abrasive polyethylene damage.

Despite initial tibiofemoral incongruity and concerns of high contact stress, round-on-flat UKR offers a durable knee arthroplasty. Delamination was infrequent and did not correlate with time in-situ. Rather, polyethylene cold flow increased the contact area during in-vivo function. Rigorous attention to cement technique and component position may reduce the incidence of abrasive damage on UKR polyethylene inserts.

There is renewed interest in unicondylar knee replacements (UKR) to meet the increasing demand for less invasive surgical procedures for knee arthroplasty. UKR survivorship exceeds 85% at 10 years, with unconstrained (round-on-flat) designs showing significantly better survivorship than conforming designs. However, round-on-flat articulations have the potential for poor wear performance and more conforming, mobile-bearing UKR designs have been advocated. This study evaluates the wear performance of unconstrained UKR polyethylene bearings retrieved at revision knee arthroplasty.

Forty-two UKR with fixed polyethylene tibial bearings were retrieved. Patient age and time in-situ averaged 73 (45–89) years and 7 (1–19) years, respectively. All knees had intact cruciate ligaments at index surgery. Revision reasons included loosening (45%), progressive arthritis (17%), polyethylene wear (17%), instability (5%), and other (17%). Retrospective radiographic review of radiolucent lines and component alignment was completed using Knee Society guidelines. Polyethylene articular damage size (% of articular surface area), location and damage mode incidence were measured using microscopy and digital image analysis.

Damage area was centrally located and averaged 65%+22%. The largest damage areas consisted of abrasion (19%) and scratching (17%). Revision for loosening or wear was significantly correlated with greater damage area (Spearman Correlation, p=0.049). The incidence of scratching, pitting and abrasion each exceeded 70%, including 29 inserts with peripheral abrasive damage consistent with impingement between the polyethylene and extra-articular cement or bone. Anterior damage location and abrasion were significantly correlated with component position (p< 0.001). Concave surface deformation due to femoral component contact was externally rotated (24 inserts), consistent with tibial external rotation relative to the femoral component, neutrally aligned (11 inserts), internally rotated (4 inserts), and indeterminate (3 inserts).

Despite initial tibiofemoral incongruity and concerns of high contact stress, round-on-flat UKR offers a durable knee arthroplasty. The relatively unconstrained tibiofemoral articulations allowed freedom of placement on the resected bone surfaces and a range of tibio-femoral rotation during activity, as demonstrated by the rotated concave surface deformations. Such deformation may reduce polyethylene contact stresses by increasing the tibio-femoral contact area. However, similar to retrieved mobile bearing UKR which show a 63% incidence of impingement, abrasive damage on these fixed bearing UKR has consequences for polyethylene debris generation and the transmission of shear forces to the bone-implant interface. Rigorous attention to conventional and minimally invasive surgical technique, including cement fixation and component position, is needed to reduce the incidence of abrasive polyethylene damage.

Introduction: Minimal-invasive techniques in total joint replacement are perceived to reduce soft tissue trauma. In TKR, reduced exposure during surgery bares the risk of component malpositioning. Therefore we have combined minimal invasive surgical techniques with non-CT based navigation in TKR. The purpose of this observational study is to describe first results of a controlled observational study comparing minimal invasive navigated total knee arthroplasty (MINI-NAV-TKR) to open navigated total knee arthroplasty (NAV-TKR) with respect to component positioning, surgery time and immediate postoperative complications.

Materials and Methods: From June to September 2004, 26 MINI-NAV-TKR and 33 NAV-TKR have been performed by five surgeons in an unselected group of patients. In both groups, preoperative deformation of the mechanical leg axis was compared to postoperative mechanical leg axis using total one-leg standing radiographs. To control the safety and reproducibility of both procedures, time of surgery and postoperative complications were compared among both groups.

Results: Given informed consent, 17 females and 9 males received 26 MINI-NAV-TKR, mean age was 71,06 years (ranging from 56,24 years to 84, 35 years), mean BMI was 28,8 kg/m2 and preoperative mechanical leg axis ranged from 18o varus to 16 o valgus. In NAV-TKR group, 12 males and 21 females at a mean age of 68,75 (range 51,97 to 86,73 years) received 33 TKR, mean BMI was 30,6 kg/m2 and preoperative mechanical axis ranged from 11 varus to 20 valgus. Postoperative radiographic leg alignment in the MINI-NAV-TKR group ranged from 1 degree valgus to 3 degree varus mechanical axis as compared to the NAV-TKR that ranged from 1 valgus to one outlayer of 4 degree varus. Time of surgery significantly differed among the groups (mean time Mini-NAV-TKR 115,23 min versus mean time NAV-TKR 98,15 minutes, p=0,002). In the MINI-NAV-TKR group 1 postoperative pin-infection and one conversion to an open procedure have been reported, in the NAV-TKR group 2 hematomas have been described.

Conclusion: Despite increased mean time of surgery in the MINI-NAV-TKR group, component positioning and complications are comparable between both groups. These preliminary results indicate, that MINI-NAV-TKR combined with navigation is a safe and reproducible method.