Constrained Condylar Knee Research Articles

Condylar constrained system in primary total knee replacement: our experience and literature review.

Constrained condylar knee (CCK) prosthesis are common used for revision surgery but can also help surgeons to improve implant stability in primary knee arthroplasty, in fact in severe knee arthrosis with serious deformity associated with a significant instability a more constrained articulation is required. With introduction of second generation of semi-constrained prosthesis, rate of complication is real decreased and a good survival rate and functional score results is showed. In this paper we write about our experience using CCK in primary knee arthroplasty. Between January 2012 and December 2015, 28 second-generation semi-constrained knee arthroplasties were performed as a first implant. Two different types of implants were used: 10 constrained condylar knee (CCK Zimmer) and 18 TC3 (DePuy Johnson & Johnson). All patients were over 75 years old (mean 81.75) with a severe deformity and clinical evaluations at 2-, 6-, 12-month after surgery and every year performed. X-rays at 6, 12 months and then annually was planned with an average follow-up of 31.28 (range 6-48) months. No patients were lost during the follow-up. The mean functional knee society score (KSS) improved from 30 points preoperatively to 92.1 points at the last follow-up. All patients recovered full extension during follow-up and no radiolucent lines were showed at X-ray control. There were no deep infections or peri-prosthetic fractures. Second generation semi-constrained knee prosthesis represent safe and practical treatment in primary total knee arthroplasty (TKA) in case of severe deformity that can't be managed with accurate soft tissue release, especially in elderly patients.

Constraint choice in revision knee arthroplasty: study protocol of a randomised controlled trial assessing the effect of level of constraint on postoperative outcome

IntroductionThe proper management of total knee arthroplasty (TKA) in patients with severe deformities regarding the preferable prosthetic design and the required amount of constraint is a controversial subject. In the...

Clinical Outcomes Following the Use of Constrained Condylar Knees in Primary Total Knee Arthroplasty

BackgroundCertain clinical or adverse intraoperative situations require the use of increased constraint in primary total knee arthroplasty (TKA). These include significant angular deformities causing incompetent collateral ligaments, or inadvertent intraoperative injury to collateral structures as well as the inability to achieve a balanced flexion and extension gap. Clinical success has been described with the use of constrained condylar knee arthroplasty in the primary setting in these situations. Traditionally, increasing constraint has been in conjunction with intramedullary stems, referred to as stemmed constrained condylar knees (SCCK); however, some devices provide an intermediary option by increasing constraint without the use of stems, herein referred to as nonstemmed constrained condylar knees (NSCCK). The aim of this study was to compare the clinical outcomes of both these devices in primary TKA in terms of revision rates and change in outcome measures over the follow-up period. MethodsBetween 2007 and 2012, 85 SCCKs and 354 NSCCKs were identified in our institutional registry database performed in the primary TKA setting with minimum 2-year clinical outcome measure follow-up. Baseline demographic information, as well as Western Ontario and McMaster Universities Arthritis Index (WOMAC) and Lower Extremity Activity Scale (LEAS) were collected preoperatively at 2-year follow-up. Revision data were also collected. ResultsBoth groups showed substantial improvement in WOMAC scores (pain, stiffness, and function), and LEAS at 2 years postoperatively compared with baseline, although the changes in scores were not statistically significant. One of 85 SCCKs (1.17%) was revised for infection, whereas 9 of 354 NSCCKs (2.54%) were revised (6 for mechanical complications, eg, loosening, 2 for periprosthetic fracture, and 1 for infection). ConclusionBoth cohorts demonstrated improvement in clinical outcome measures at 2-year follow-up. None of the SCCKs performed in the primary setting were revised for a mechanical complication. Although both groups had overall low revision rates, there was trend toward a higher revision rate with NSCCKs. Many of these were revised for component loosening. In summary, when necessary, constrained options in the primary TKA setting provide excellent clinical outcome at short-term follow-up. However, constrained constructs with stemmed fixation may provide more rigid fixation and be less susceptible to mechanical failure.

Evaluation of the Morphology and Function of Medial Collateral Ligament afterTotal Knee Arthroplasty with High-frequency Ultrasound.

Objective To explore the feasibility and clinical value of ultrasonography in evaluating the morphology and function of medial collateral ligaments (MCL) after total knee arthroplasty (TKA). Methods Totally 38 patients undergoing routine KTA (group A) and 22 patients undergoing constrained condylar knee arthroplasty KTA with MCL injury (group B) were included. Long axis views of MCL were taken and the MCL thickness was measured on femur side and tibial side 1 cm away from the joint line, respectively. The thicknesses were compared between the two groups. Subsequently, the gap between the metal part of the femoral prosthesis and the spacer after dynamic valgus stress was measured. The distribution and composition of the gap between the two groups were compared. Results High-frequency ultrasound clearly showed the prosthesis and MCL after TKA. MCL fiber structures of both groups were intact. The MCL thickness on the tibial side in group B was (0.25±0.06)cm, which was significantly thinner than group A [(0.32±0.14)cm] (t=2.12, P=0.040).For the femur side, there was no significant difference (t=1.65, P=0.110) between these two groups [(0.37±0.09) cm in group B versus (0.42±0.12)cm in group A]. Under the condition of valgus stress, the gaps between the metal part of the femoral prosthesis and the spacer could be found in 11 cases in group B but only in 1 case in group A. The proportion of gaps in group B was significantly higher than that in group A (Fisher's exact test, P=0.000). Conclusions High-frequency ultrasound can clearly show the prosthesis and MCL after TKA. The injured MCL can be well joined but the thickness is thinner. Under the condition of valgus stress of the knee, the stability of the TKA can be evaluated according to the gap between the prosthesis and the spacer.

Load Sharing Among Collateral Ligaments, Articular Surfaces, and the Tibial Post in Constrained Condylar Knee Arthroplasty.

The normal knee joint maintains stable motion during activities of daily living. After total knee arthroplasty (TKA), stability is achieved by the conformity of the bearing surfaces of the implant components, ligaments, and constraint structures incorporated in the implant design. The large, rectangular tibial post in constrained condylar knee (CCK) arthroplasty, often used in revision surgery, provides added stability, but increases susceptibility to polyethylene wear as it contacts the intercondylar box on the femoral component. We examined coronal plane stability to understand the relative contributions of the mechanisms that act to stabilize the CCK knee under varus-valgus loading, namely, load distribution between the medial and lateral condyles, contact of the tibial post with the femoral intercondylar box, and elongation of the collateral ligaments. A robot testing system was used to determine the joint stability in human cadaveric knees as described by the moment versus angular rotation behavior under varus-valgus moments at 0 deg, 30 deg, and 90 deg of flexion. The angular rotation of the CCK knee in response to the physiological moments was limited to ≤1.5 deg. The primary stabilizing mechanism was the redistribution of the contact force on the bearing surfaces. Contact between the tibial post and the femoral box provided a secondary stabilizing mechanism after lift-off of a condyle had occurred. Collateral ligaments provide limited stability because little ligament elongation occurred under such small angular rotations. Compressive loads applied across the knee joint, such as would occur with the application of muscle forces, enhanced the ability of the bearing surfaces to provide resisting internal varus-valgus moment and, thus, reduced the exposure of the tibial post to the external varus-valgus loads. Our results suggest that the CCK stability can be refined by considering both the geometry of the bearing surfaces and the contacting geometry between the tibial post and femoral box.

Results of a Second-generation Constrained Condylar Prosthesis in Complex Primary and Revision Total Knee Arthroplasty: A Mean 5.5-Year Follow-up.

Background:The application of second-generation constrained condylar knee (CCK) prostheses has not been widely studied. This retrospective study was carried out to evaluate the clinical and radiographic outcomes of a second-generation CCK prosthesis for complex primary or revision total knee arthroplasty (TKA).Methods:In total, 51 consecutive TKAs (47 patients) were performed between June 2003 and June 2013 using second-generation modular CCK prostheses. The follow-up was conducted at 3rd day, 1st, 6th, and 12th months postoperatively and later annually. Anteroposterior (AP), lateral, skyline, and long-standing AP radiographs of the affected knees were taken. The Hospital for Special Surgery (HSS) Knee Score, the Knee Society Knee Score (KSKS), the Knee Society Function Score (KSFS), and range of motion (ROM) were also recorded. Heteroscedastic two-tailed Student's t-tests were used to compare the HSS score and the Knee Society score between primary and revision TKAs. A value of P < 0.05 was considered statistically significant.Results:Four knees (two patients) were lost to follow-up, and 47 knees (31 primary TKAs and 16 revision TKAs) had a mean follow-up time of 5.5 years. The mean HSS score improved from 51.1 ± 15.0 preoperatively to 85.3 ± 8.4 points at the final follow-up (P < 0.05). Similar results were observed in terms of the KSKS and KSFS, which improved from 26.0 ± 13.0 to 80.0 ± 12.2 and from 40.0 ± 15.0 to 85.0 ± 9.3 points, respectively (P < 0.05). No significant difference in the HSS, KSKS, KSFS, or ROM was found between primary and revision TKAs (P > 0.05). Two complications were observed in the revision TKA group (one intraoperative distal femur fracture and one recurrence of infection) while one complication (infection) was observed in the primary TKA group. No prosthesis loosening, joint dislocation, patella problems, tibial fracture, or nerve injury were observed. Radiolucent lines were observed in 4% of the knees without progressive osteolysis.Conclusions:Second-generation modular CCK prostheses are a safe and practical treatment for both primary and revision knees that cannot be balanced. However, further studies focusing on different types of constrained prostheses are required to validate these results.

Grafted Vitamin-E UHMWPE may increase the durability of posterior stabilized and constrained condylar total knee replacements.

The suitability of grafted vitamin-E highly crosslinked polyethylene (VE-HXPE) for use in posterior stabilized (PS) and constrained condylar knee (CCK) applications has not been explored. We hypothesized that VE-HXPE performs better than conventional and crosslinked polyethylene under clinically relevant conditions. PS tibial post fracture resistance under adverse shear loading conditions, CCK tibial post resistance to torsional fatigue, delamination resistance under high stress, and wear resistance were evaluated. Grafted VE-HXPE exhibits (1) 10% and 57% improved PS post fatigue strength compared to conventional PE (CPE) and remelted HXPE; (2) 45% improved CCK post fatigue strength compared to CPE; (3) Greater than 36× the delamination resistance of CPE; and (4) 96% and 73% wear reduction compared to CPE and HXPE. VE-HXPE performed well under clinically relevant in vitro conditions. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1789-1798, 2017.

Total knee arthroplasty revision with trabecular tantalum cones: Preliminary retrospective study of 51 patients from two centres with a minimal 2-year follow-up

BackgroundSuccessful management of large bone defects is of crucial importance when performing revision total knee arthroplasty (TKA). Trabecular tantalum cones may improve prosthesis fixation via their potential for reconstructing a stable metaphyseal support. The objective of this study was to evaluate the clinical and radiological outcomes and the complications of tantalum cones in revision TKA. HypothesisTrabecular tantalum cones provide stable and durable metaphyseal reconstruction when used during revision TKA. Material and methodsTrabecular Metal™ cones (Zimmer, Warsaw, IN, USA) were used for 52 revision TKAs in 51 patients (mean age, 68±9 years) managed in two centres between 2008 and 2013. A rotating hinge prosthesis was chosen for 38 (73%) knees and a condylar constrained knee prosthesis for 14 (27%) knees, with 37 tibial and 34 femoral cones. The two most common reasons for revision surgery were aseptic loosening (n=22, 42%) and infection (n=19, 37%). The bone loss was severe in most cases. At each centre, after a mean follow-up of 34 months (range, 24–52 months), two independent observers assessed the Knee Society Score (KSS), range of motion, mechanical axis, and osteo-integration for each patient. ResultsMean KSS increased from 46 preoperatively to 77 (P=0.001) at last follow-up and the mean KSS function from 39 to 57 (P=0.007). Mean range of motion improved from 93° (45°–120°) to 110° (65°–130°) (P=0.001). Mean postoperative mechanical axis was 180° (172°–190°). Radiographic evaluation showed evidence of osteo-integration for all cones. Four revisions were performed for recurrence of infection but none for mechanical failure. DiscussionThe findings of our study confirm the biomechanical and biological reliability of Trabecular Metal™ cones used to fill metaphyseal bone defects during revision TKA. Level of evidenceIV, retrospective therapeutic study.

Primary modular total knee replacement in severe and unstable osteoarthritis. Predictive factors for failure.

Severe cases of osteoarthritis with ligamentous instability require the use of a modular knee arthoplasty. To assess the survival, the complications, the clinical, radiological and functional outcomes, and the quality of life of those patients in whom a Optetrak Condylar Constrained Knee (CCK) had been implanted as a primary implant. To study how the pre-operative conditions (deformity, age, sex …) and the characteristics of the arthroplasty (stems, supplements, constrained component …) could change the survival or the clinical outcomes of the implants. We performed an observational retrospective study of 105 CCKs implanted between 1999 and 2005. The mean follow-up was nine years (7, 13). Mean age was 70.5 years. The mortality was 6.9 %. There were 9.3 % of the patients lost during the follow-up. We studied all the medical files of the patients in order to assess the pre-operative, surgical and postoperative conditions. We used the Knee Society Score (KSS), both clinical and functional, to study the functional and clinical situation. We analysed the X-ray using the Knee Society roentgenographic evaluation. The quality of life was studied using the Oxford Knee Score (OKS). Then in order to find predictor conditions, we made statistical multivariable predictive studies attending to the preoperative factors and to the arthroplasty conditions to compare both outcomes and survival (Kaplan-Meier groups curves and Cox Multivariable Models [hazard ratio]). Processing and data analysis was performed using SPSS 15.0. The outcomes did not show differences between all the groups. While the mean result of the clinical KSS was 75.8, the mean functional KSS was 73.1. We did not find a condition associated with worst results of the knees (p > 0.05). The KSS obtained was excellent or good in 74.9 %. The global survival at 24 months was 93.8 % and at 96 months was 90.1 %. There were some conditions associated with poorest survival of the arthroplasties: patients younger than 70 years old, tibial tuberosity osteotomy, use of long stems and new surgery two months after arthoplasty (p < 0.05). The 11.1 % of the arthroplasties required more surgeries (3.3 % were soft tissue surgeries and 7.8 % were revisions). The mean OKS obtained was 34.78. Satisfaction was obtained by 86.2 % of the patients. All severe and unstable knees obtained similar and overall excellent-good outcomes and survival using the Optetrak CCK. Although we found that there are some factors that could change the survival of the total knee replacement, these did not change the outcomes.

Long-term outcomes of primary constrained condylar knee arthroplasty

BackgroundAlthough constrained condylar knee (CCK) inserts are widely used for total knee arthroplasty (TKA), their long-term outcomes remain unclear. We sought to evaluate patients with at least 10 years’ follow-up after CCK TKA to identify potential adverse events (osteolysis, loosening, constraint-mechanism failure), assess functional outcomes with special emphasis on range of motion, and determine prosthesis survival. HypothesisIncreasing constraint by implantation of a CCK insert does not increase the long-term frequencies of osteolysis or mechanical loosening. Material and methodsWe studied 43 knees after Legacy® CCK TKA. The indication was severe deformity (n=20), pre-operative laxity (n=6), or failure to achieve intra-operative balancing (n=17). There were 41 patients with a mean age of 66 years (21–88). A history of one or more surgical procedures was noted for 27 (63%) knees. Outcome measures were the Hospital for Special Surgery (HSS) knee score, Knee Society Score (KSS), and change in the hip-knee-ankle (HKA) angle. Prosthesis survival was assessed using revision surgery for any reason or for reasons other than infection as the censoring criterion. ResultsComplications other than venous thrombosis occurred in 16% of patients, including 3 who required revision surgery (septic loosening, n=2; and major instability in a patient with ipsilateral hip arthrodesis). No cases of osteolysis or aseptic loosening were recorded. Mean follow-up was 12.7 years (range, 10–14). At last follow-up, the HSS score had improved from 53 (26–83) pre-operatively to 80 (55–93), the KSS knee component from 42 (16–77) to 90 (77–99), and the KSS function component from 31 (0–80) to 61 (10–90) (P<0.001). Mean range of flexion increased from 109° (50°–140°) to 112° (90°–130°) (P=0.12). The HKA angle changed from 182°±15.5° (150°–210°) to 179.5°±2.5° (174°–184°) (P=0.5). The 11-year prosthesis survival rate was 88.5% (95% confidence interval, 0.69–0.94) overall and 97.7% (0.76–0.99) after excluding the cases of infection. DiscussionLong-term functional gains after CCK TKA were similar to those reported after standard posterior-stabilised TKA, with no cases of constraint-mechanism failure or osteolysis. The complication rate was higher, with decreased survival compared to standard TKA, but the knee deformities and/or instability were particularly severe and two-thirds of knees had a history of one or more surgical procedures. Level of evidenceLevel IV, retrospective case-series study.

Long-Term Clinical Outcomes and Survivorship of Revision Total Knee Arthroplasty with Use of a Constrained Condylar Knee Prosthesis

The purpose of this study was to determine long-term clinical and radiographic results. One hundred and ninety-four patients (228 knees) underwent revision TKA with use of a constrained condylar knee prosthesis. The mean duration of follow-up was 14.6years (range, 11 to 16years). The mean pre-revision Knee Society knee scores (43.5 points) and function scores (47.0 points), and Western Ontario and McMaster Universities Osteoarthritis index scores (88 points) were improved significantly (P=0.002) to 85.6, 68.5, and 25 points, respectively, at 14.6years follow-up. Eighteen knees (8%) had re-revision. Four knees were re-revised for infection. Kaplan–Meier survivorship analysis revealed that the 16-year rate of survival of the components was 94.7% as the end point of loosening and 92% as the end point of revision.

2- to 9-year outcome of stemmed total knee arthroplasty

Background and purpose — There is an increase in demand for primary and revision total knee joint procedures. We studied implant survival and functional outcome of patients operated with a constrained condylar knee (CCK) or a rotating hinge implant (RH) as a primary or a revision total knee arthoplasty (TKA).Patients and methods — We evaluated clinically and radiographically 65 surgical procedures with a mean follow-up time of 5 (2–9) years (40 CCK and 25 RH). There were 24 primary TKAs—due to instability—and 41 revision TKAs, mostly due to aseptic loosening. Mean age at the index operation was 68 (31–88) years.Results — Overall, there were 12 failures, including 8 reoperations due to deep infection. The overall 5-year survival rate with reoperation as the endpoint was 82% (95% CI: 72–99). Radiolucent lines on either the femoral or the tibial side were seen in 36 cases. When comparing the cases that were operated as a primary TKA or as a revision TKA, function, health-related quality of life, and survival were similar. However, after primary TKA the patients generally had less pain and a higher proportion of patients were very satisfied or satisfied.Interpretation — Although a high rate of severe complications was observed, most patients improved in function after surgery regardless of whether it was a primary or a revision TKA. We found narrow radiolucent lines—mainly on the tibial side—in nearly half of the cases, but none of the implants were loose radiographically. Overall patient satisfaction and health-related quality of life were high, and a minority had problems with persistent pain.

Survival of Primary Condylar-Constrained Total Knee Arthroplasty at a Minimum of 7 Years

The purpose of the present study is to retrospectively analyze clinical and radiographic outcomes in primary constrained condylar knee arthroplasty at a minimum follow-up of 7years. Given the concern for early aseptic loosening in constrained implants, we focused on this outcome. Our cohort consists of 127 constrained condylar knees. The mean age of patients in the study was 68.3years, with a mean follow-up of 110.7months. The diagnosis was primary osteoarthritis in 92%. There were four periprosthetic distal femur fractures, with a rate of revision of 0.8%. No implants were revised for aseptic loosening. Kaplan–Meier survivorship analysis with removal of any component as the end point revealed that the 10-year rate of survival of the primary CCK was 97.6% (95% CI, 94%–100%).

Range of motion and function are not affected by increased post constraint in patients undergoing posterior stabilized total knee arthroplasty

BackgroundConstrained primary total knee arthroplasty (TKA) can provide stability in the face of incompetent collateral structures or irreconcilable flexion–extension imbalances. However, little is known about its effect on overall knee range of motion (ROM). This study determines whether TKA with increased constraint affects postoperative ROM. MethodsPatients undergoing primary TKA using either posterior stabilized (PS) or constrained condylar knee (CCK) inserts were match-paired based on body mass index, preoperative ROM, and direction and severity of the coronal deformity, yielding 68 pairs. ROM and Knee Society Score (KSS) were obtained preoperatively and at 6weeks, 4months, and 1year. ResultsWhen the 68 matched pairs were considered, all outcome variables related to ROM between the PS and CCK groups at each of the postoperative intervals were similar. Additionally, both the individual items and combined scores of the KSS were similar between groups at all time points. ConclusionsWe demonstrate that the use of increased constraint does not affect ROM, relief of pain, or function after TKA. Level of evidenceLevel III (retrospective case-controlled study, based on prospectively collected data).

Revision Total Knee Arthroplasty Using a Constrained Condylar Knee Prosthesis in Conjunction with A Posterior Stabilized Articular Polyethylene

Legacy constrained condylar knee (LCCK) components are designed in the way that they can also be used in conjunction with a posterior-stabilized (PS) polyethylene insert, when adequate collateral stability is present. This study comprised 27 revision total knee arthroplasties (TKA) treated using an LCCK prosthesis and a PS polyethylene insert. Substantial range of motion and Knee Society score improvements were achieved in all subjects. Radiolucent lines between the block-cement were noted in 6 of 27 knees, but not significant. During TKA requiring the use of a femoral augment or stem extension, the design offering least constraint can be chosen, and an LCCK prosthesis with a PS polyethylene insert could be a satisfactory option.

One-stage total knee arthroplasty for patients with osteoarthritis of the knee and extra-articular deformity

The purpose of this paper is to review our experience and study the feasibility and clinical results of one-stage total knee arthroplasty (TKA) for patients with osteoarthritis of the knee with extra-articular deformity. Nine patients with osteoarthritis of the knee associated with extra-articular deformity underwent one-stage TKA from June 2006 to April 2010. There were two men and seven women, with an average age of 51years (range 34-69years); four of them had tibial deformities and five had femoral deformities. Eight of the cases resulted from malunion after fracture healing and one from femoral recurvatum. Six of the cases had uniplanar and three had biplanar deformities. The average angles of the femoral deformities were 13.3° in the coronal plane (8-22) and 11.3° in the sagittal plane (6-15); one femur had 10° external rotational deformity. Tibial deformity of 16° in the coronal plane (11-22) was noted, and one had sagittal plane deformity of 21°. All patients were followed for an average of 29months. The average Hospital for Special Surgery (HSS) knee score improved from 18.7 points pre-operatively to 89.8 points at the time of last follow-up; the range of knee motion improved from 46.7° preoperatively to 100.6° postoperatively. The average angle of mechanical axis deviation was restored from 11.8° preoperatively to 1° postoperatively. One of the patients had unsatisfactory clinical results due to delayed union at the osteotomy site. No complications such as infection, deep vein thrombosis, ligament instability, low level or subluxed/dislocated patella or component loosening were observed. One-stage TKA with intra-articular correction of the extra-articular deformity was performed in seven patients, included proper planning, appropriate bone cuts to restore alignment and the necessary soft tissue releases to balance the knee in flexion and extension. Two patients underwent simultaneous extra-articular correctional osteotomy and TKA because the deformity was so large. Five knees that had good collateral ligamentous stability and balance received a posterior stabilised prosthesis; four knees that had ligamentous instability received a constrained condylar knee (CCK) prosthesis. One-stage TKA is a technically difficult but effective treatment for patients with osteoarthritis of the knee and extra-articular deformity. If feasible we recommend TKA with intra-articular bone resection and soft tissue balancing.

Clinical Results and Failure Mechanisms of a Nonmodular Constrained Knee Without Stem Extensions

In the setting of persistent knee instability despite appropriate ligament balancing for primary total knee arthroplasty, most surgeons advocate the use of an implant with increased articular constraint. These implants are commonly supplemented with stem extensions to improve stress transfer and decrease the risk of aseptic loosening. However, disadvantages exist with the use of stem extensions, including increased cost, intramedullary invasion, and diaphyseal pain. The objectives of this study were to (1) compare the clinical results as assessed by the Knee Society, Hospital for Special Surgery, and SF-12 scores, (2) determine the incidence of failure as defined by the need for a revision procedure, and (3) to analyze the causes or modes of failure of a nonmodular constrained condylar knee without the use of stem extensions versus a conventional, posterior-stabilized design. From 2002 to 2007, 190 TKAs were implanted using a primary, nonmodular constrained (NMC) prosthesis without stem extensions. During the same time period, clinical data were available for 140 TKAs implanted using a standard, posterior-stabilized (PS) design. Preoperative demographic data was reviewed, in addition to the rate and reason for revision in each cohort. Clinical data included HSS, Knee Society, and SF-12 scores at the latest follow-up, and the results of the NMC and PS cohorts were statistically compared using a Student's two-tailed t test. The mean age of patients in the NMC cohort was 72.3 ± 10.2years, and the mean length of follow-up was 7.3 ± 2.1years. The mean age of the PS cohort was 67.1 ± 8.7years, with a mean follow-up of 6.1 ± 2.2years. No statistically significant differences in the HSS, Knee Society, or SF-12 scores were appreciated between the two cohorts. The revision rate in the NMC cohort was 4.2% compared to 4.3% for the PS cohort. The most common cause of failure in the NMC cohort was femoral component loosening, all of which occurred when Palacos cement was used for fixation. NMC components (55.6%) implanted with Palacos cement failed due to femoral component loosening. In contrast, all PS components requiring revision were revised for persistent instability. At mid-term follow-up, NMC prostheses without stem extensions have excellent clinical results and are a viable option for patients with ligamentous instability. The use of Palacos cement in this scenario was associated with a high rate of femoral component loosening, possibly due to the decreased intrusion depth of Palacos when compared to Simplex cement.

Results of a Second-Generation Constrained Condylar Prosthesis in Primary Total Knee Arthroplasty

This is a prospective study of the results of a second-generation modular constrained condylar knee (CCK) prosthesis in primary total knee arthroplasty. Of 418 consecutive total knee arthroplasties performed by 1 surgeon, a second-generation modular CCK prosthesis was indicated for intraoperative stability in 30 knees (7.2%). Three knees were lost to follow-up, and 27 knees had a mean follow-up time of 5.4 years (range, 2-11.5 years). All tibial components had a cemented 35-mm stem extension, and 26 femoral components had a 100-mm uncemented stem extension. The indication for use of the CCK components was most commonly severe valgus deformity and incompetent medial collateral ligament. There were no revisions for loosening, patella problems, or tibial post fracture. A lateral retinacular release of the patella was performed in 6 knees (22%). An asymptomatic, minimally displaced patella fracture was noted in 2 knees (7.4%). Constrained condylar knees are used infrequently now but are successful for the treatment of the unstable primary knee that cannot be balanced. These results may be design specific.

Computer-Assisted Revision of Failed Unicompartmental Knee Arthroplasty

The authors performed a matched-paired study comparing 22 computer-assisted surgery (CAS)-unicompartmental knee replacement (UKR) revisions with a similar group of knee replacement revisions performed conventionally. The aim of the study was to assess differences in implants used in the revision, surgical time, limb alignment, joint line restoration, and procedure costs. In the conventional group, there was a higher percentage of posterior stabilized (PS) and condylar constrained knee (CCK) implants, as well as a higher percentage of augmentations/stems/offsets. There were no statistically significant differences in postoperative mechanical axis, surgical time, or hospital stay. There were fewer outliers and better joint line restoration in the CAS group. More blood transfusions were performed in the conventional group, and costs were higher in this group as well.

Constrained Condylar Knee Without Stem Extensions for Difficult Primary Total Knee Arthroplasty

Two hundred forty-eight constrained condylar total knee arthroplasties consecutively implanted without the use of diaphyseal stem extensions were studied in 180 patients. Preoperative deformity was severe (82% Ahlbäck grade 4-5). One hundred ninety-two knees (148 patients) were reviewed at mean 47-month follow-up (range: 24-72 months). Knee Society score improved from 36 to 89 points, and function score improved from 42 to 76 points. Failure rate was 2.5% (2 infections, 1 aseptic loosening, 1 supracondylar femoral fracture, and 1 tibial post fracture). Five (2.5%) knees had patellofemoral complications. Nonprogressive radiolucent lines were present in 16% of cases. Use of a nonmodular constrained condylar knee for primary severely damaged knees demonstrated reliable short- to mid-term results with a low complication rate and questioned the routine use of intramedullary stem extensions in all such cases.