Factors contributing to inherent varus alignment of lower limb in normal Asian adults: Role of tibial plateau inclination

PurposeThis prospective study aimed to evaluate radiographically, mechanical or hip–knee–ankle (HKA) axis in healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to determine the incidence of inherent varus (mechanical limb alignment of > 3° varus) and the factors influencing it.MethodsThree hundred and eighty-eight lower limbs were evaluated using full length, standing hip-to-ankle radiographs in 198 healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to assess the hip–knee–ankle (HKA) angle, medial proximal tibial angle (MPTA), femoral bowing and femoral neck–shaft angle to determine the incidence of inherent varus (mechanical limb alignment of > 3° varus) and the factors influencing it.ResultsOverall, the mean HKA angle was 177.6° ± 2.6° with 34.5% of limbs in inherent varus (mean HKA angle 174.9° ± 1.8°). The incidence of inherent varus was significantly higher (p = 0.01) in males (40%) compared to females (28%) but similar among Indian (34%) and Korean subjects (35%). The hip–knee–ankle (HKA) angle showed significant positive correlation (r = 0.82, p < 0.001) with only the medial proximal tibial angle (MPTA).ConclusionsInherent varus alignment of the lower limb is fairly common among asymptomatic, Asian adults. These results raise several pertinent questions regarding the role of inherent varus in the aetiopathogenesis of knee osteoarthritis and in lower limb realignment procedures.     

Comparison between navigated reported position and postoperative computed tomography to evaluate accuracy in a robotic navigation system in total knee arthroplasty

BackgroundComputer navigation increases reproducibility compared to non-navigated total knee arthroplasty (TKA). Robotics navigation is a branch of computer navigation technology that might further improve accuracy of implant placement. The aim of this study is to assess the accuracy achieved in TKA with a robotic navigation system.MethodsOne hundred seventy three knees. System studied: Omni navigation System (OMNI, Raynham, MA). Navigated femoral and tibial cuts were compared to postoperative computed tomography (CT). Measurements reviewed: femoral coronal alignment (FCA), femoral sagittal alignment (FSA), femoral rotational alignment (FRA), tibial coronal alignment (TCA), tibial sagittal alignment (TSA) and hip–knee–ankle (HKA) angle. Statistical analysis was made using R.ResultsThe mean differences between the navigated reported and the CT positions were: FCA: 0.1 ± 1.2° more varus (P = 0.58), FSA: 1.5 ± 0.3° more flexed (P < 0.001), FRA: 0.0 ± 1.7° (P = 0.93), TCA: 0.7 ± 1.1° more varus (P < 0.001), TSA: − 1.3 ± 1.5 more negative slope (P < 0.001), HKA angle: 0.4 ± 2.4 more varus (P < 0.049).The percentages of concordance inside a three degree difference were: FCA: 98% (169 knees), FSA: 100% (173 knees), FRA: 94% (162 knees), TCA: 99% (171 knees), TSA: 93% (161 knees) and HKA angle: 83% (144 knees).ConclusionsThe current study showed that the robotic navigation system studied is highly accurate regarding final implant positioning for FCA, FRA and TCA. It has less accuracy in FSA, TSA and the HKA angle.     

The tibial crest as a practical useful landmark in total knee arthroplasty

BackgroundThe middle one-third of the tibial crest in the coronal plane and the fibula in the sagittal plane are known as landmarks for extramedullary guides in total knee arthroplasty (TKA). However, there are few foundational anatomic studies about them. We conducted this study to confirm whether these landmarks are reliable.MethodsWe evaluated 100 Japanese knees using 3D imaging software. We examined our data for correlations between the angle of deviation from the mechanical axis and patient-specific factors (i.e. hip-knee-ankle angle, tibial length, tibial bowing, and tibial torsion) to determine whether there are any individual factors affecting their reliability.ResultsThe mean angles between each of the axes defined by the fibula and the tibial crest with the mechanical axis were 2.9° ± 0.6° of valgus and 0.7° ± 0.9° of varus in the coronal plane and 2.2° ± 0.8° of posterior and 3.6° ± 1.0° of anterior inclination in the sagittal plane. The middle one-third of the tibial crest (TCL) was revealed as a useful landmark, especially in female patients, who possess TCLs that were within 3° of the tibial mechanical axis in the coronal plane. There were no patient-specific factors strongly affecting reliability of these landmarks.ConclusionsWe can use these landmarks even if the patient has tibial bowing or severe varus deformity. Although not considering soft tissue thickness, our study demonstrated that the tibial crest in the coronal and sagittal planes could be useful guidelines in performing TKAs.Level of evidenceII     

The value of the intra-operative clinical mechanical axis measurement in open-wedge valgus high tibial osteotomies

IntroductionIn high tibial osteotomies (HTO) the correction needs to be precise and intra-operative assessment is essential. The purpose of this study was to evaluate the use of the intra-operative clinical mechanical axis measurement and compare it to the post-operative weight bearing situation on standing whole leg radiographs (WLR). Secondly, we evaluated the preoperative planned wedge size and compared it to the final results in 27 HTOs.MethodsThe mechanical axis deviation (MAD), expressed as a percentage of the tibial width (0% is medial edge, 100% is lateral edge) and the hip–knee–ankle angle (HKA) were calculated and analyzed. Preoperative planning was done by projecting the desired mechanical axis on the lateral tibial spine on the WLR and subsequently calculating the necessary correction angle. A 3° valgus correction was desired.ResultsThe results showed a preoperative standing MAD of 26.6%, or about halfway the medial tibial plateau. The MAD was corrected to 57.0% intra-operative, meaning a slight valgus. On the postoperative standing WLR, the MAD had shifted significantly to 62.0% (95% CI = ? 9.2 to ? 2.7; p < 0.01) compared to the intra-operative 57.0% axis. The HKA angle changed 8.2° from 5.1° varus preoperative to 3.1° valgus postoperative.ConclusionWhen aiming the mechanical axis at the lateral tibial spine, a slight undercorrection was introduced, but due to a valgus shift while weight bearing, a satisfying final outcome of 3° valgus average was achieved. Preoperative calculation of the wedge size remains important for surgical planning, but it does not always correspond to the actual used wedge size.     

Effect of tibial component varus on wear in total knee arthroplasty

IntroductionMalalignment can result in poor clinical outcomes and increased wear. However, component malalignment can occur even when overall limb mechanical axis is within the normal anatomic range. We studied the effect of component malalignment in the presence of acceptable knee alignment in knee arthroplasty.MethodsSixteen tibial inserts retrieved at revision surgery were laser-mapped to measure wear. Average implantation duration was 7.7 years (range, 1 to 13). Early (postprimary) and final (prerevision) radiographs were analyzed for overall alignment (limb, femoral and tibial components) and osteolysis.ResultsThe tibial components were initially aligned in a mean of 1.3 ± 1.7° varus (range, –1.5 to 4.5°), which increased to 3.2 ± 2.9° (range, –2.0 to 8.0°) at the time of revision (p = 0.05). Tibial components initially placed in greater than 3° varus were associated with almost twice the volumetric penetration rate. Anatomic knee angles were 5.4 ± 0.9° valgus (range, 4.0 to 7.0°) in the post-primary radiographs and decreased in prerevision radiographs to 3.8 ± 2.6° (range, –1.0 to 7.5°), (p = 0.04).DiscussionTibial varus was associated with increased medial compartment wear and total wear, thus affecting osteolysis in addition to local destruction of the bearing surface. Varus malalignment as low as 3° may result in accelerated wear, even if overall limb alignment is nearly ideal. These results indicate that tibial component alignment is an important factor associated with tibial tray subsidence and polyethylene wear even when limb alignment is neutral.     

Referencing the substitute anteroposterior line of the tibia improves rotational alignment of the tibial component in medial unicompartmental knee arthroplasty

BackgroundThere is no consensus regarding how best to determine the tibial rotational alignment in unicompartmental knee arthroplasty (UKA). The purpose of this study was to clarify whether using the substitute anteroposterior (sAP) line of the tibia, as has recently been proposed, can improve tibial rotation.MethodsThe study included 57 consecutive medial UKAs. From May 2015 to September 2016, 28 knees in 28 patients underwent UKA using the medial intercondylar ridge (MIR) line as the tibial anteroposterior (AP) reference (MIR group). From October 2016 to March 2018, 29 knees in 29 patients underwent UKA using the sAP line (sAP group). In both groups, the external rotation angle of the tibial component relative to a line perpendicular to the surgical epicondylar axis was measured using computed tomography-based three-dimensional preoperative planning software for TKA and UKA.ResultsThe mean external rotation angles of the tibial component in the MIR and sAP groups were 5.2° ± 8.5° (range, − 12.4° to 20.8°) and 0.7° ± 3.2° (range, − 6.0° to 7.4°), respectively (unpaired t test, P = 0.014). The variation in the external rotation angle of the tibial component was significantly smaller in the sAP group than in the MIR group (F test, P < 0.0001), as was the number of the outliers with more than ± 5° error (Fisher's exact test, P < 0.0001).ConclusionsThe use of the sAP line as the AP reference could improve and stabilize the rotational orientation of the tibial component in UKA procedures.     

胫骨髁外翻截骨术治疗创伤性膝关节炎的早期临床疗效分析

目的 探讨胫骨髁外翻截骨术（TCVO）治疗陈旧性内侧胫骨平台骨折并发创伤性膝关节炎（TKOA）的早期临床疗效。方法 回顾性分析2016年6月至2021年6月于苏州市立医院关节外科接受TCVO手术治疗陈旧性内侧胫骨平台骨折并发TKOA的18例患者的术前及术后相关临床资料,所有患膝均为陈旧性内侧胫骨平台骨折保守治疗后畸形愈合并发膝内翻TKOA。患者发生胫骨平台骨折至TCVO手术治疗的时间为49 ～ 171个月,平均（111.1±33.8）个月;患膝内翻角度为6.81° ～ 14.49°,平均10.95°±2.62°;关节线会聚角（JLCA）为3.58° ～ 8.12°,平均5.95°±1.42°。所有患者于术前及术后3个月拍摄站立位双下肢全长X线片、膝关节正侧位X线片并测量患膝内翻角度、胫骨近端内侧角（MPTA）、JLCA、胫骨平台后倾角（PTS）,评估术前、术后下肢力线以及膝关节对合状态的变化情况。依据术前及术后3、12个月的患膝关节活动度（ROM）、疼痛视觉模拟评分（VAS）、西安大略与麦克马斯特大学（WOMAC）骨关节炎指数、膝关节损伤与骨关节炎评分（KOOS）评估早期临床疗效。结果 18例患者均获得随访,随访时间为14 ～ 65个月,平均随访（27.4±14.4）个月。术后3个月时,患膝内翻角、JLCA均较术前显著降低,差异均具有统计学意义（P＜0.05）;MPTA与术前相比有显著提升,差异有统计学意义（P＜0.05）;PTS与术前相比差异无统计学意义（P＞0.05）。术后3、12个月时,患膝关节ROM、VAS、WOMAC、KOOS评分均较术前有显著好转,差异均具有统计学意义（P＜0.05）。结论 采用TCVO治疗陈旧性内侧胫骨平台骨折并发TKOA可以取得良好的早期临床疗效,有效矫正膝关节内翻畸形,缓解膝关节疼痛及改善膝关节功能。     

The in vivo relationship between anterior neutral tibial position and loss of knee extension after transtibial ACL reconstruction

BackgroundRestoration of anterior tibial stability while avoiding knee extension deficit are a common goal of anterior cruciate ligament (ACL) reconstruction. However, achieving this goal can be challenging. The purpose of this study was to determine whether side-to-side differences in anterior tibial neutral position and laxity are correlated with knee extension deficit in subjects 2 years after ACL reconstruction.MethodsIn the reconstructed and contralateral knees of 29 subjects with transtibial reconstruction, anterior tibiofemoral neutral position was measured with MRI and three-dimensional modeling techniques; terminal knee extension at heel strike of walking and during a seated knee extension were measured via gait analysis; and anterior laxity was measured using the KT-1000.ResultsKnees that approached normal anterior stability and anterior tibial position had increased extension deficit relative to the contralateral knee. On average the reconstructed knee had significantly less (2.1 ± 4.4°) extension during active extension and during heel strike of walking (3.0 ± 4.3º), with increased anterior neutral tibial position (2.5 ± 1.7 mm) and anterior laxity (1.8 ± 1.0 mm). There was a significant correlation between side-to-side difference in anterior neutral tibial position with both measures of knee extension (walking, r = − 0.711, p < 0.001); active knee extension, r = − 0.544, p = 0.002).ConclusionThe results indicate a relationship between the loss of active knee extension and a change in anterior neutral tibial position following non-anatomic transtibial ACL reconstruction. Given the increasing evidence of a link between altered kinematics and premature osteoarthritis, these findings provide important information to improve our understanding of in vivo knee function after ACL reconstruction.     

Accuracy of a hand-held surgical navigation system for tibial resection in total knee arthroplasty

BackgroundAccuracy of total knee arthroplasty (TKA) implant placement and overall limb are important goals of TKA technique.MethodsThe accuracy and ease of use of an accelerometer-based hand-held navigation system for tibial resection during TKA was examined in 90 patients. Preoperative goals for sagittal alignment, navigation system assembly time, resection time, and tourniquet time were evaluated. Coronal and sagittal alignment was measured postoperatively.ResultsThe average coronal tibial component alignment was 0.43° valgus; 6.7% of patients had tibial coronal alignment outside of ± 3° varus/valgus. The difference between the intraoperative goal and radiographically measured posterior tibial slope was 0.5°. The average time to completion of the tibial cut was 4.6 minutes.ConclusionThe accelerometer-based hand-held navigation system was accurate for tibial coronal and sagittal alignment during TKA, with no additional surgical time compared with conventional instrumentation.     

The influence of tibial morphology on the design of an anatomical tibial baseplate for TKA

BackgroundFinding the right balance between tibial coverage and minimal implant overhang is an important factor in TKA. Another significant cause of failure is component malrotation.MethodsAn average master shape of the proximal tibia at TKA resection level was calculated using fine slice computed tomographies of 117 cadaveric knees. To find out whether alternate implant contours would be necessary depending on the patient's body size, we established five subgroups to compare. CAD-Analysis was performed to simulate the overhang produced after ± 4°/± 7°/± 10° rotation.ResultsA master shape for the tibial resection cut (with a 5° posterior slope, 7 mm under lateral joint line) could be determined. Neither left vs. right knee joint, nor male vs. female nor the size subdivision appears to alter the calculated master shape significantly. The optimized shape allowing for ± 4° of rotational freedom was found to be the best variant.ConclusionsValid methods have been obtained to design a two-dimensional average shape of the tibial plateau. The modifications described in this study might come in useful, when designing future implant designs.Clinical relevanceAn optimized fit at the tibial plateau and lower rates of component malrotation may result in better outcomes after TKA.     

Double-level osteotomy for severe varus osteoarthritic knees can prevent change in leg length and restore physiological joint geometry

BackgroundIt is unclear whether double-level osteotomy (DLO) combining closed-wedge osteotomy in the distal femur and open-wedge osteotomy in the proximal tibia deformity can prevent change in leg length and excessive coronal inclination of the tibial articular surface in surgical correction of the severe varus knee. The purpose of this study was to examine the postoperative change in leg length as well as radiological and clinical outcomes following DLO compared with the results obtained from knees undergoing isolated open-wedge high tibial osteotomy (OW-HTO).MethodsIn cases of severe varus knee deformity (hip–knee–ankle angle (HKA) > 10°) 29 patients undergoing DLO and 35 patients undergoing OW-HTO were included. If the predicted mechanical medial proximal tibial angle (mMPTA) was 95° or greater or the wedge size was 15 mm or greater in the surgical simulation, then DLO was considered as the surgical of option. In cases where these criteria were not met, OW-HTO was selected. All patients were followed up for a minimum of 2 years.ResultsThe changes in the length of the whole leg in the DLO and OW-HTO groups averaged 2.3 ± 4.8 mm and 9.3 ± 7.2 mm, respectively (P < 0.001). mMPTA of more than 95° was found in no knee in the DLO group.ConclusionsThis study showed that DLO could avoid leg length change and non-physiologic joint lines when performed in patients with varus HKA > 10°, and the predicted mMPTA was 95° or greater or the wedge size was 15 mm or greater in the surgical simulation.     

Focal proximal fibular angle: A potential indicator of the tibial mechanical axis in opening-wedge high tibial osteotomy

BackgroundFor opening-wedge high tibial osteotomy, correct alignment is essential for a better prognosis. It is difficult to evaluate the mechanical axis of the lower extremity or tibia using a single fluoroscopic image. This study aimed to discuss the use of focal proximal fibular angle (FPFA), which can be assessed by a single fluoroscopic image, as an intraoperative indicator.MethodsEligible for analyses were 111 consecutively treated patients; for the final analyses 96 patients were included. The preoperative and postoperative medial proximal tibial angle (MPTA) and FPFA were measured. The relationship between these two angles, correction amount, weight-bearing line ratio and patient characteristics were analyzed.ResultsThe preoperative FPFA and MPTA were 96.5 ± 3.8° (mean ± standard deviation, SD) and 84.8 ± 3.0°, while the postoperative FPFA and MPTA were 87.6 ± 4.1° and 94.0 ± 3.5°, respectively. The preoperative and postoperative sums of the MPTA and FPFA were constant. The discrepancy was less than 3° in all knees, less than 2° in 92.7% knees and less than 1° in 68.8% knees. It was not correlated with age, sex, weight-bearing line ratio, or correction amount.ConclusionThe study findings confirmed the constancy of the sum of the MPTA and FPFA. The FPFA can be easily evaluated on a single fluoroscopic image of the knee. Use of the FPFA as guidance may simplify the procedure of opening-wedge high tibial osteotomy and approximately predict the tibial mechanical axis.     

Aligning the tibial component with medial border of the tibial tubercle—is it always right?

IntroductionCorrect rotational alignment of the tibial component is crucial for total knee arthroplasty (TKA). Several studies have indicated that the best rotational orientation of the tibial component is close to the medial border of the tibial tubercle. However, it remains obscure whether it is always right. Thus, the objective of current study was to quantify tibial rotational alignment in 120 primary rotating platform TKAs using the medial border of tibial tubercle as a landmark between July 2008 and June 2010.MethodsThe femoral component was positioned parallel to the transepicondlylar axis, and a rotating platform trial insert was used to determine tibial insert rotational alignment relative to the most medial aspect of the tibial tubercle with the knee in full extension. Rotational alignment of the components was detected based on radiograph and CT scan. This investigation is based on the premise that all neutral points would lie within 10° of the mean.ResultsThe mean divergence external to the medial border of the tubercle was 2.3° ± 3.5°. However, six of the knees (5%) had neutral points ≥ 10° from the mean, including two valgus knees measured 10° of internal rotation and four varus knees measured 10° of external rotation.ConclusionUsing the medial border of tibial tubercle as a landmark does not always result in a good femoro-tibial rotational alignment. Surgeons using fixed bearings component should be aware of this effect to avoid suboptimal outcomes resulting from tibiofemoral rotational malalignment in full extension.Level of evidenceDiagnostic study, Level II-3.     

In vivo kinematic analysis of posterior-stabilized total knee arthroplasty for the valgus knee operated by the gap-balancing technique

BackgroundMost in vivo kinematic studies of total knee arthroplasty (TKA) report on the varus knee. The objective of the present study was to evaluate in vivo kinematics of a posterior-stabilized fixed-bearing TKA operated on a valgus knee during knee bending in weight-bearing (WB) and non-weight-bearing (NWB).MethodsA total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis and that were operated on using the gap balancing technique were evaluated. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimensional to 3-dimensional registration technique.ResultsThe average flexion angle was 111.3° ± 7.5° in WB and 114.9° ± 8.4° in NWB. The femoral component demonstrated a mean external rotation of 5.9° ± 5.8° in WB and 7.4° ± 5.2° in NWB. In WB and NWB, the femoral component showed a medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion. The medial condyle moved similarly in the WB condition and in the NWB condition. The lateral condyle moved posteriorly at a slightly earlier angle during the WB condition than during the NWB condition.ConclusionsWe conclude that similar kinematics after TKA can be obtained with the gap balancing technique for the preoperative valgus deformity when compared to the kinematics of a normal knee, even though the magnitude of external rotation was small. Level of evidence: IV.     

The effect of component alignment on clinical outcomes in fixed bearing unicompartmental knee arthroplasty

BackgroundThe aim of this study is to report component alignment in a series of ZUK fixed bearing unicompartmental knee arthroplasty (UKA) implants and compare this to clinical outcomes.MethodsThe radiographs, Knee Society Scores (KSS) and knee flexion of 223 medial UKAs were evaluated. The following alignment parameters were assessed; coronal and sagittal femoral component angle (c-FCA and s-FCA), coronal and sagittal tibia component angle (c-TCA and s-TCA) and the coronal tibiofemoral angle (c-TFA). Each alignment parameter was grouped at consecutive 2.5° intervals, mean KSS and knee flexion was then compared between the interval groups.Results96.4% of femoral components were between 7.5° of varus and valgus and 95.1% between 7.5° extension and 5° flexion. 89.6% of tibial components were between 7.5° of varus and 2.5° valgus and 97.3% between 2.5° and 15° flexion. There was no significant difference between the KSS or knee flexion between any of the incremental groups of component alignment. Mean c-TFA was 0.2 ± 3.0°, 92.4% were between −5° (varus) and 5° (valgus). KSS were significantly greater for two of the increments with slightly more varus. Linear regression analysis showed there was very weak correlation (R² = 0.1933) between c-TFA and c-TCA.ConclusionsThe results of this study show that fixed bearing UKA components are forgiving to accommodate some variation in tibial and femoral component position without effecting clinical outcome scores or knee flexion. Limb alignment matters more than component position and knees with slight varus tibiofemoral alignment have better clinical scores than those with valgus.     

Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty

IntroductionIn total knee arthroplasty, the accuracy and precision of the tibial resection must be improved. The purpose of this study was to determine the accuracy and time associated with the use of an accelerometer based, extramedullary surgical navigation system for performing the tibial resection.Materials and methodsFour orthopedic surgeons performed a tibial resection utilizing the KneeAlign? system, each on five separate, cadaveric tibiae. Each surgeon was assigned a preoperative “target” of varus/valgus alignment and posterior slope prior to each resection. The alignment of each resection was measured using both plain radiographs and computed tomography, along with the time required to use the device.ResultsRegarding coronal alignment, the mean absolute difference between the preoperative “target” and tibial resection alignment was 0.77° ± 0.64° using plain radiograph, and 0.68° ± 0.46° using CT scan measurements. Regarding the posterior slope, the mean absolute difference between the preoperative “target” and the tibial resection was 1.06° ± 0.59° using plain radiograph, and 0.70° ± 0.47° using CT scan measurements. The time to use the KneeAlign? for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study.DiscussionThis cadaveric study demonstrates that the KneeAlign? system is able to accurately align the tibial resection in both the coronal and sagittal planes.Level of evidenceCadaveric study.     

Estimation of frontal alignment error of the extramedullary tibial guide on the bi-malleolar technique: A simulation study with magnetic resonance imaging

PurposeThe bi-malleolar technique for the extramedullary tibial guide is a representative method for determining the ankle center in total knee arthroplasty (TKA). The purpose of this study is to estimate three-dimensionally the lateral errors (difference between the real ankle center and the bi-malleolar center) and the varus angular errors of this technique under the condition that the malleolar prominences were correctly identified.MethodsMagnetic resonance images of 51 lower limbs from 51 healthy volunteers were analyzed. The lateral errors were measured, including or excluding the subcutaneous thickness, along the line perpendicular to the transmalleolar axis (TMA) or along the tibial anteroposterior (AP) axis. Furthermore, we evaluated the effects of the tibial torsion and the difference between the subcutaneous thicknesses on the malleoli on the lateral error.ResultsWhen including the skin, the mean lateral errors of the ankle center observed along the line perpendicular to the TMA and along the tibial AP axis were 3.7 ± 1.4 mm and 1.2 ± 1.5 mm, respectively. The mean angular errors were 0.6 ± 0.2° and 0.2 ± 0.3°, respectively. A significant correlation between the tibial torsion and the lateral error was noted when observed along the tibial AP axis. The difference between the subcutaneous thicknesses on the malleoli affected the lateral error.ConclusionThe errors were small enough to determine the mechanical axis of the tibia if the tibial guide could catch the bi-malleolar prominences of the ankle accurately and align along the tibial AP axis.     

Effect of femoral to tibial varus mismatch on the contact area of unicondylar knee prostheses

In unicondylar knee prostheses, the relative angle and congruency of the femoral against the tibial component is not mechanically constrained and may vary with the surgical implantation technique.The contact area between both components was measured with increasing varus (0–20°) and flexion angles (? 20° to 90°) in five prosthesis models in the laboratory.The contact area varied with the relative position of the components and was critically reduced up to 70% at a varus range between > 5° and < 25°.The importance of relative malpositioning of the femoral and tibial components may be underestimated and reduces the contact area of unicondylar prostheses decisively, independent from the limb axis. This increases local pressure and may thus importantly contribute to increased wear and early loosening.     

Unicompartmental knee arthroplasties: Robot vs. patient specific instrumentation

BackgroundThe technical reliability demonstrated by semi active robots in implant placement could render unicompartmental knee arthroplasties (UKAs) more favourable than they are currently. The relatively untested method using patient specific instrumentation (PSI), however, has the potential to match the accuracy produced by robots but without the barriers that have prevented them from being used more widely in clinical practice, namely operative time. Therefore this study took a step towards comparing the accuracy and time taken between the two technologies.MethodsThirty-six UKAs were carried out on identical knee models, 12 with the Sculptor, 12 with PSI and 12 conventionally under timed conditions. Implant placement in these knees was then judged against that in a pre-operative plan.ResultsTibial implant orientations and femoral implant positions and orientations were significantly more accurate in the PSI group with mean errors of 6°, 2 mm and 4° respectively, than the conventional group which had means of 9°, 4 mm and 10°. There was no significant difference between the robot and PSI generally except in tibial implant orientation (mean robotic error 3°) and tibial implant position did not vary significantly across all three groups. It was also found that use of PSI and conventional methods took half the time taken by the robot (p < 0.001).ConclusionsWith further development, PSI can match and possibly surpass the accuracy of the robot, as it does with the conventional method, and achieve planned surgery in less time.Clinical relevanceThis work sets the foundation for clinical trials involving PSI.