Soft Tissue Balancing Research Articles

Assessment of accuracy of an imageless hand-held robotic-assisted system in component positioning in total knee replacement: a prospective study

In recent years, robotic technology is becoming more pervasive in joint arthroplasty. The role of robotics in joint replacement surgery is to bring precision and accuracy in bone preparation, implant positioning and soft tissue balancing. However, there is yet to be a study conducted to determine the accuracy of bone preparation done by a new robotic system. The purpose of this study is to evaluate and report on the accuracy of bone cuts using imageless semiautonomous freehand robotic sculpting system, Navio (Smith & Nephew) based on the data provided by the robotic system. Between August 2018 and May 2019, a total of 62 patients were prospectively enrolled in this study. All surgeries were done by the senior author using a medial para-patellar approach and using a posterior stabilised implant (Anthem, Smith & Nephew Inc.). The study included 37 female patients and 25 male patients. The parameters assessed in this study were: (1) mechanical axis, (2) femoral coronal alignment, (3) femoral rotation, (4) femoral sagittal alignment, (5) tibial slope and (6) tibial coronal alignment using paired t test and root mean squared error (RMSE). The robotic system was accurate in achieving the bone cuts as planned in mechanical axis alignment (p = 0.89, RMSE = 0.56), femoral coronal alignment (p = 0.36, RMSE = 0.36), femoral sagittal alignment (p = 0.10, RMSE = 0.44), femoral rotation (p = 0.91, RMSE = 0.11), tibial coronal alignment (p = 0.81, RMSE = 0.24) and tibial slope (p = 0.30, RMSE = 0.37) with the maximum RMSE being 0.56. This study demonstrated that semi-autonomous hand-held robotic system, Navio (Smith & Nephew) for total knee arthroplasty produced accurate component positioning as per plan in all planes. The maximum RMSE was 0.56°.

Gama angle in sagittal plane of post-operative total knee replacement - variations in patients: A retrospective radiological analysis

Introduction: Total Knee Replacement (TKR) though appears as bone surgery, but success depends on correct pre-operative analysis, better execution of bone cuts and soft tissue balancing. Radiological evaluation shows differences between patients, even though same instrumentation and technique were used in surgery. There appears variation in Gama angle in femur, posterior slope in tibia. Aim and Objectives: To analyze variability of Gama angle in patients after post TKR surgery. To find out the reasons of variability of Gama angle, posterior slope and sagittal femoral bowing Materials and Methods: A retrospective study carried out in Department of Orthopedics, BIRRD (T) Hospital. All the surgeries were carried out by single surgeon were included into the study after satisfying inclusion and exclusion criteria. The study involves radiological evaluation, without direct interaction of patient. Patients were evaluated for basic radiological measurements in coronal and sagittal planes. Results were tabulated and evaluated. Results: Seventy-two patients were included into study. There were 30, 42 male and female patients respectively. 54 patients with unilateral and 18 patients bilateral TKR were carried. Average age of patient was 61 years. Average Gama angle in femoral side, posterior slope in tibia and femoral sagittal femoral bowing was 4o, 85.4o and 5.5o respectively. Conclusion: There exists positive co-relation in femoral bowing, posterior slope in tibia and Gama angle in femur in sagittal plane radiologically.

The effect of glenoid lateralization and glenosphere size in reverse shoulder arthroplasty on deltoid load: A biomechanical cadaveric study

PurposeUse of a relatively larger glenosphere with some larger overhang helps to minimize posterior impingement and some degree of glenoid lateralization is also beneficial in reverse shoulder arthroplasty (RSA). The optimal amounts of inferior overhang and lateralization are not agreed upon. The purpose of this in-vitro biomechanical study is to analyze the effect of glenosphere size and glenoid lateralization on deltoid load, focusing on differences in its three distinct heads. MethodsReverse shoulder arthroplasty (DeltaXtend, Fa. Depuy/Synthes) was performed on six cadaveric specimens. The load on each head of the deltoid muscle (spinalis, acromialis, and clavicularis) was measured indirectly by transferring deformation (μm/m) via strain gauges (Fa. Vishay) with stepwise lateralization: +0 mm (subgroup I), +5 mm (subgroup II), +10 mm (subgroup III). Each scenario was done with a 38 mm (group A) and a 42 mm (group B) glenosphere. ResultsIn group A as well in group B, the mean measured deformation in the respective titanium omega increased with lateralization in the clavicular (AI: 119.6 μm/m, AIII: 307.3 μm/m; BI: 173.3 μm/m, BIII: 358.5 μm/m), in the spinal (AI: 85.3 μm/m, AIII: 188.5 μm/m; BI: 138.8 μm/m, BIII 261.2 μm/m) and in the acromial head (AI: 340.5 μm/μ; AIII: 454.2 μm/m; BI: 388.5 μm/m, BIII: 538.8 μm/m). A significant difference between the subgroups in the spinal (p = .048) and clavicular heads (p = .028) was found. The use of a 42 mm glenosphere increased significantly the load in each segment. ConclusionLateralization and glenosphere size increased significantly deltoid muscle loading, especially in the clavicular head. According to these in-vitro data, the high variability in the amount of lateralization influences the soft-tissue balance in reverse shoulder arthroplasty. Level of evidenceBasic science study.

Outcome of technique of total knee arthroplasty by independent total femoral first followed by tibial cuts as a measured resection based on anatomical landmarks along with scientific soft tissue balancing: A surgicoclinical study

Introduction: Total knee arthroplasty is one of the commonest musculoskeletol pain relieving surgery now a days. The long legacy of the different surgical techniques attracts the orthopaedic surgeons to opt for better results oriented techniques. Since in the mid 19s of origin of early knee arthroplasty to 2014 of gap balancing vs measured resection technique from US to the recent navigation & robotics era, different study showed improved results. For developing countries with financial constrains cost effective & results oriented more studies warranted. Objectives: To study the results of all femoral cuts first followed by tibial cuts as a measured resection technique based on anatomical landmarks followed by scientific soft tissue balancing for total knee arthroplasty. Materials and Methods: We have analyzed total (n= 126) the total knee replacement surgeries operated by our team during last 48 months retrospectively. Mean age was 66 years. All the Knee arthritis classified by Kellgren & Lawrence classification preoperatively. Results were evaluated by Oxford knee score (OKS). Results: According to OKS 92.91% had excellent to good results & 7.09% had fair to poor results (95% CI).Out of fair to poor results group 33.56% patients were 65 years of age. Conclusion: Total femur first followed by tibial measured resection cuts based on anatomical landmarks backed up with scientific soft tissue balancing & admission of all the other disciplines for total knee arthroplasty is a results oriented technique for increasing burden of operative patients & decreasing social morbidity. Keywords: Knee arthroplasty, Soft tissue balancing, Anatomical land marks, Arthritis, Femur first.

In Vivo Elongation Patterns of the Collateral Ligaments in Healthy Knees During Functional Activities.

Improved knowledge of in vivo function of the collateral ligaments is essential for enhancing rehabilitation and guiding surgical reconstruction as well as soft-tissue balancing in total knee arthroplasty. The aim of this study was to quantify in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities. Knee kinematics were measured using radiographic images captured with a mobile fluoroscope while healthy subjects performed level walking, downhill walking, and stair descent. The registered in vivo tibiofemoral kinematics were then used to drive subject-specific multibody knee models to track collateral ligament elongation. The elongation patterns of the medial collateral ligament varied distinctly among its bundles, ranging from lengthening of the anterior fibers to shortening of the posterior bundle with increases in the knee flexion angle. The elongation patterns of the lateral collateral ligament varied considerably among subjects. It showed an average 4% shortening with increasing flexion until 60% to 70% of the gait cycle, and then recovered during the terminal-swing phase until reaching its reference length (defined at heel strike). The observed nonuniform elongation of the medial collateral ligament bundles suggests that single-bundle reconstruction techniques may not fully restore healthy ligament function. Moreover, the observed ligament elongation patterns indicate greater varus than valgus laxity in the loaded knee. Through providing key knowledge about the in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities, this study offers in vivo evidence for benchmarking ligament reconstruction and soft-tissue balancing in total knee arthroplasty.

Accuracy of total knee arthroplasty using the modified gap technique based on the bone gap: an evaluation of the bone gap with a distal femoral trial component

BackgroundIn total knee arthroplasty (TKA) using the modified gap technique, the soft-tissue balance is measured after osteotomy of the distal femur and proximal tibia (conventional bone gap). However, after osteotomy, the flexion gap size during 90° knee flexion may be larger than that observed after implantation. The tension of the lateral compartment during 90° flexion may also be reduced after osteotomy of the distal femur. We manufactured a distal femoral trial component to reproduce the condition after implantation and prior to posterior condyle osteotomy. This study aimed to evaluate the effect of the trial component on the flexion gap.MethodsThis prospective study included 21 consecutive patients aged 78 years with medial osteoarthritis who underwent cruciate-retaining TKA between February 2017 and March 2018. The postoperative flexion gap size and inclination during 90° flexion were compared between cases with and without the trial component.ResultsThe mean joint gap size with the trial component (13.4 ± 0.80 mm) was significantly smaller than that without the trial component (14.7 ± 0.84 mm). The mean gap inclination angle with the trial component (3.7° ± 0.62°) was significantly smaller than that without the trial component (5.5° ± 0.78°).ConclusionsIn the present study, the joint gap size and medial tension were significantly reduced after the trial component had been set. Accurate measurement of the soft-tissue balance is an important factor in the modified gap technique, and this method using a distal femoral trial component can offer better outcomes than those achieved with conventional methods.

Modern femoral component design in total knee arthroplasty shows a lower patellar contact force during knee flexion compared with its predecessor

BackgroundThe relationship between the femoral component design in total knee arthroplasty (TKA) and the patellofemoral contact force, as well as the soft tissue balance, has not been well reported thus far. MethodsTwenty-eight mobile-bearing posterior-stabilized (PS) TKAs using the traditional model (PFC Sigma) and 27 mobile-bearing PS TKAs using the latest model (Attune) were included. Surgeries were performed using the measured resection technique assisted with the computed tomography (CT)-based free-hand navigation system. After all the trial components were placed, patellar contact forces on the medial and lateral sides were measured using two uniaxial ultrathin force transducers with the knee at 0°, 10°, 30°, 60°, 90°, 120°, and 135° of flexion. The joint component gap and the varus ligament balance of the femorotibial joint were also measured. The non-paired Student’s t-test was conducted to compare the values of the two groups. ResultsThe medial patellar contact force was significantly lower for Attune group than for PFC Sigma group at 120° of knee flexion (P = 0.0058). The lateral patellar contact force was also significantly lower for Attune group than PFC Sigma group at 120° and 135° of knee flexion (P = 0.0068 and P = 0.036). The joint component gap, as well as the varus ligament balance, showed no statistically significant difference between the two groups. ConclusionsReduced thickness and width of the anterior flange of the femoral component in the Attune may play a role in low patellar contact force.

The Functionality of a Novel Robotic Surgical Assistant for Total Knee Arthroplasty: A Case Series

Conventional total knee arthroplasty and soft tissue balancing is based on a subjective unquantified assessment, which can lead to imperfect balancing and poor patient outcomes. Five case studies were used to present the functionality of a novel robotic system in allowing intraoperative adjustments based on objective measures for several primary total knee arthroplasty cases. The robotic system allows the surgeon to drive every step of the case, turning the subjective nature of conventional knee replacement into a more objective and scientific approach for restoration of alignment, gap balancing, joint space restoration, femoral rotation, and Q-angle restoration. The robotic system allowed precise intraoperative adjustments, as demonstrated by these cases, and is a promising step towards more personalized total knee arthroplasty made possible by utilizing real-time objective measures.

Biomechanical Consequences of Tibial Insert Thickness after Total Knee Arthroplasty: A Musculoskeletal Simulation Study

The thickness of the tibial polyethylene (PE) insert is a critical parameter to ensure optimal soft-tissue balancing in the intraoperative decision-making procedure of total knee arthroplasty (TKA). However, there is a paucity of information about the kinetic response to PE insert thickness variations in the tibiofemoral (TF) joint, and subsequently, the secondary effects on the patellofemoral (PF) biomechanics. Therefore, the purpose of this study was to investigate the influence of varying PE insert thickness on the ligament and TF compressive forces, as well as on the PF forces and kinematics, after a cruciate-retaining TKA. A previous patient-specific musculoskeletal model of TKA was adapted to simulate a chair-rising motion in which PE insert thickness was varied with 2 mm increments or decrements compared to the reference case (9 mm), from 5 mm up to 13 mm. Greater PE insert thickness resulted in higher ligament forces and concurrently increased the TF compressive force by 21% (13 mm), but slightly unloaded the PF joint with 7% (13 mm) while shifting the patella distally in the trochlear groove, compared to the reference case. Thinner PE inserts showed an opposite trend. Our findings suggest that the optimal PE insert thickness selection is a trade-off between the kinetic outcomes of the TF and PF joints.

Functional alignment achieves soft-tissue balance in total knee arthroplasty as measured with quantitative sensor-guided technology.

Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology. This prospective study included 30 consecutive patients undergoing robotic-assisted TKA using the Stryker PS Triathlon implant with functional alignment. Intraoperative soft-tissue balance was assessed using sensor-guided technology after definitive component implantation; soft-tissue balance was defined as intercompartmental pressure difference (ICPD) of < 15 psi. Medial and lateral compartment pressures were recorded at 10°, 45°, and 90° of knee flexion. This study included 18 females (60%) and 12 males (40%) with a mean age of 65.2 years (SD 9.3). Mean preoperative hip-knee-ankle deformity was 6.3° varus (SD 2.7°). TKA with functional alignment achieved balanced medial and lateral compartment pressures at 10° (25.0 psi (SD 6.1) vs 23.1 psi (SD 6.7), respectively; p = 0.140), 45° (21.4 psi (SD 5.9) vs 20.6 psi (SD 5.9), respectively; p = 0.510), and 90° (21.2 psi (SD 7.1) vs 21.6 psi (SD 9.0), respectively; p = 0.800) of knee flexion. Mean ICPD was 6.1 psi (SD 4.5; 0 to 14) at 10°, 5.4 psi (SD 3.9; 0 to 12) at 45°, and 4.9 psi (SD 4.45; 0 to 15) at 90° of knee flexion. Mean postoperative limb alignment was 2.2° varus (SD 1.0°). TKA using the functional alignment achieves balanced mediolateral soft-tissue tension through the arc of knee flexion as assessed using intraoperative pressure-sensor technology. Further clinical trials are required to determine if TKA with functional alignment translates to improvements in patient satisfaction and outcomes compared to conventional alignment techniques. Cite this article: Bone Joint J2021;103-B(3):507-514.

Functional results and quality of life after joint preserving or sacrificing surgery in Charcot-Marie-Tooth foot deformities.

The purpose of this study was to assess the functional results, quality of life, and complications in two groups of Charcot-Marie-Tooth (CMT) patients according to the type of surgical operations, joint preserving, or joint sacrificing surgery. Fifty-two feet in forty-six patients with CMT who had undergone surgical deformity correction were divided into two groups based on the main surgical procedure for the correction: Class I (joint preserving surgery) and class II (joint sacrificing surgery). Foot ankle disability index (FADI) and short form 12 version 2 (SF12V2) were documented pre-operative and 12 months post-operative. The complications of both groups were monitored with a mean follow-up time of 20.5 months (range, 13-71.5). After surgical treatment, FADI scores showed differences (p=0.005) between both groups. The functional improvement was 29 (20-46; p<0.001) in class I and 10 (2-36; p=0.001) in class II. The patients in both groups acquired a better quality of life as demonstrated in physical component summary of SF12 but without statistically difference. Three feet needed reintervention in class I (two for cavovarus recurrence and one for hallux flexus) at the end of follow-up. In contrast, five feet needed a new operation for cavovarus recurrence, claw toes recurrence, and ankle osteoarthritis after the progression of the condition. An early surgical intervention to neutralize the deforming forces in CMT patients could be a useful strategy to delay or prevent the need for extensive reconstruction and potential future complications. Based on the type of surgical intervention in CMT patients, the joint preserving surgery in addition to soft tissue balancing procedures obtained better functional outcomes and lower rate of complications when compared to the group of joint sacrificing surgery.

Single-stage total knee arthroplasty and femoral osteotomy for osteoarthritis with severe supracondylar deformity

BackgroundKnee osteoarthritis associated with extra-articular deformity (EAD) can confront the arthroplasty surgeons with challenges of bone resection and soft tissue balancing. The aim of this study was to describe a single-stage procedure associating corrective osteotomy with total knee arthroplasty (TKA), and to determine the outcome at mid- to long-term follow-up.MethodsA total of seven patients (seven knees) with knee osteoarthritis and supracondylar deformity were included in this study. Six patients were female, and one was male, with the median age of 62 years (range, 37-76 years). All patients were treated with single-stage TKA and femoral osteotomy. Osteotomy was fixed with long cemented stem. Hospital of Special Surgery (HSS) scores, collateral ligament laxity, and range of motion (ROM) were clinically evaluated preoperatively and at each follow-up. Radiographic parameters including the mechanical axis deviation (MAD), mechanical lateral distal femoral angle (mLDFA), mechanical proximal tibial angle (mMPTA), and joint line congruence angle (JLCA) were also measured. The occurrence of perioperative complications was recorded.ResultsThe median follow-up time was 91 months (range, 38-104 months). At the last follow-up, all components were stable and no patients required revision. Nonunion of the osteotomy occurred in one patient. In all patients, the lower limb mechanical alignment improved greatly. The mean angle of MAD was restored from 10.49±6.05 cm preoperatively to 1.11±4.97 cm postoperatively. The 90° mLDFA was almost acquired in all cases, with the postoperative value of 90.79±2.40°. After operation, the mMPTA improved from 84.18±6.13° to 91.33±3.13°. The JLCA changed from 2.94±1.61° to −0.71±3.50°. The median HSS score improved from 45 (range, 34-56) preoperatively to 90 (range, 82-97) postoperatively, with the outcome of all patients rated good to excellent. The median ROM improved from 70° (range 0–110°) preoperatively to 105° (range 90–125°) postoperatively. No instability of knee joint was observed. Complications included an intraoperative split fracture of distal femur and one case of wound exudation resulting from fat liquefaction.ConclusionsFor knee osteoarthritis with femoral supracondylar deformity, single-stage TKA and corrective osteotomy was feasible but technically demanding. The use of long cemented stem for osteotomy fixation can provide reliable rotational control of the bone segments.

Evaluation of the pathological anatomy of posteromedial corner in varus osteoarthritic knees using magnetic resonance imaging

BackgroundUnderstanding the pathological changes in varus osteoarthritic knees will help the surgeon to correct the deformity while performing total knee arthroplasty. The currently available MRI resolution allows us to recognize the anatomical details of the posteromedial corner and the changes associated with osteoarthritic knees. The study aims to assess the pathological changes of the varus osteoarthritic knees on MRI and to compare it to non-arthritic knees. MethodsMRI of 26 patients with varus osteoarthritic knees (Kellgren and Lawrence grade 4) scheduled for total knee arthroplasty were reviewed and compared to MRI of 10 other patients without knee arthritis. The superficial Medial Collateral Ligament (sMCL) was assessed in terms of medial and posterior bowing, and the posteromedial corner (PMC) was evaluated in terms of thickness and signal integrity. ResultsThe superficial Medial Collateral Ligament (sMCL) was medially and posteriorly displaced in all severely varus arthritic knees compared to its position in non-arthritic knees, in addition to significant increase in posteromedial corner thickness with heterogenous appearance indicating scarring in the posteromedial corner (PMC). (p-value lower than 0.05). ConclusionThe apparent tightness of the superficial Medial Collateral Ligament can be secondary to the pathology that affects the posteromedial corner (scarring) where sMCL is retracted and bowed posteriorly and medially, not simply contracted and shortened. Understanding the pathological changes of severely varus osteoarthritic knees on MRI can lead to a better algorithm to perform soft tissue balance during Total knee replacement surgery without releasing sMCL and subsequent knee instability.

Robotic-assisted vs conventional surgery in medial unicompartmental knee arthroplasty: a clinical and radiological study

BackgroundThe use of unicompartmental knee arthroplasty (UKA) has increased and new technologies have been developed to improve patient survival and satisfaction, soft tissue balance, alignment, and component size. Robot-assisted systems offer an increase in surgical precision and accuracy. The purpose of this study is to evaluate the precision of component position using five radiological parameters in conventional and robotic-assisted medial UKA using the NAVIO system.MethodsA cohort study was designed for patients who underwent medial UKA between April 2017 and March 2019 in a single center. Patients were allocated in the conventional (UKA-C) or robotic-assisted (UKA-R) group. The variables analyzed were age, gender, affected knee side, length of hospital stay, surgical time, and radiological measurements such as anatomical medial distal femoral angle (aMDFA), anatomical medial proximal tibial angle (aMPTA), tibial slope, the sagittal femoral angle, and the component size. A target was defined for each measurement, and a successful UKA was defined if at least four radiological measures were on target after surgery. Also, patients’ reported outcomes were evaluated using the Oxford Knee Score (OKS) and a numeric rating scale (NRS) for pain.ResultsThirty-four patients were included, 18 of them underwent UKA-R. The success rate for UKA in the UKA-R group was 87%; meanwhile, in the UKA-C group this was 28%, this difference was significant and powered (Fisher’s exact test, p = 0.001; 1 − β = 0.95). Also, a 5-point difference in favor of the UKA-R group in the median OKS (p = 0.01), and a significantly lower median NRS for pain (p < 0.000) were found after surgery.ConclusionsUKA-R achieved more precision in the radiological parameters’ measure in this study. Also, UKA-R has a trend towards a better OKS and a lower NRS for pain at short-term follow-up.

Improved total knee arthroplasty pain outcome when joint gap targets are achieved throughout flexion.

Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the definition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midflexion, and flexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout flexion. 135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacrificing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90N from 10°-90° flexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to define clinically relevant joint gap target thresholds in extension, midflexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets. Significant linear correlations were found throughout extension, midflexion, and flexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1mm compared to the final insert thickness in midflexion, and a medio-lateral imbalance of less than 1.5mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisfied (median ∆ = 11.2, p = 0.002). Gap thresholds identified in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacrificing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed. Level II.

The medial gap is a reliable indicator for intraoperative soft tissue balancing in posterior-stabilized total knee arthroplasty

BackgroundAppropriate soft tissue balance and accurate alignment are important for successful total knee arthroplasty (TKA). However, the optimal technique for establishing and measuring soft tissue balancing remains unclear. The aim of this study was to analyze the intraoperative medial and lateral gap pattern using digital knee balancer in posterior-stabilized (PS) TKA. MethodsThis study involved 55 patients with medial osteoarthritis who underwent a primary TKA using an image-free navigation system. The extension gap and the flexion gap at 90° knee flexion were assessed using an offset seesaw-type digital balancer. Continuous joint distraction force from 10 lb to 60 lb was applied. Medial gap, lateral gap, and varus angle were measured. ResultsThe medial bone gap difference between extension and flexion was constant regardless of the distraction force from 20 lb to 60 lb. The lateral bone gap was significantly greater than the medial bone gap in extension and flexion from 30 lb to 60 lb (P < 0.05). The varus angle changed depending on the distraction force, especially in flexion. The varus angle in flexion was significantly greater than that in extension from 40 lb to 60 lb (P < 0.05). ConclusionsThe medial bone gap is a reliable indicator unaffected by the distraction force during surgery and is useful for adjusting the medial gap in extension and flexion appropriately to ensure medial stability in PS-TKA. The digital knee balancer and navigation system support both precise gap assessment and surgery.

Coronal Plane Alignment of the Knee (CPAK) classification.

AimsA comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA).MethodsA radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type.ResultsThere was similar frequency distribution between healthy and arthritic groups across all CPAK types. The most common categories were Type II (39.2% healthy vs 32.2% OA), Type I (26.4% healthy vs 19.4% OA) and Type V (15.4% healthy vs 14.6% OA). CPAK Types VII, VIII, and IX were rare in both populations. Across all CPAK types, a greater proportion of KA TKAs achieved optimal balance compared to MA. This effect was largest, and statistically significant, in CPAK Types I (100% KA vs 15% MA; p < 0.001), Type II (78% KA vs 46% MA; p = 0.018). and Type IV (89% KA vs 0% MA; p < 0.001).ConclusionCPAK is a pragmatic, comprehensive classification for coronal knee alignment, based on constitutional alignment and JLO, that can be used in healthy and arthritic knees. CPAK identifies which knee phenotypes may benefit most from KA when optimization of soft tissue balance is prioritized. Further, it will allow for consistency of reporting in future studies.Cite this article: Bone Joint J 2021;103-B(2):329–337.

Soft-Tissue Balancing in Total Hip Arthroplasty.

Appropriate total hip arthroplasty (THA) reconstruction must simultaneously address component position, restoration of biomechanics, and soft-tissue balance. Preoperative planning for complex THA cases should include radiographic templating, a detailed case plan that contains backup implant options, and a thorough understanding of the patient's preoperative examination. Using a systematic approach to soft-tissue balancing in THA enhances the ability to intraoperatively execute the preoperative plan. In patients with preexisting deformities (e.g., dysplasia or prior surgery), increased attention to abductor function is necessary when assessing acetabular component placement and offset.

Assessment of Motion Loss in the Thrower's Shoulder

The overhead throwing motion is a complex movement which requires soft tissue flexibility and neuromuscular control to generate force from the legs and trunk and propel the ball forward. Repetitive motions and high levels of torque on the shoulder can compromise soft tissue balance and contribute to the high rate of shoulder injuries commonly seen in throwers. A thorough physical examination including inspection of the entire kinetic chain and total arc of shoulder motion is important in making an accurate diagnosis. Nonoperative treatment with a formal progressive rehabilitation program is typically effective in treating the thrower's shoulder. Occasionally, patients may require operative intervention for posterior inferior capsular release for refractory capsular contracture, and selective treatment of superior labrum tears or rotator cuff tears when nonoperative management has been exhausted. A decrease in a thrower's total arc of motion may be more detrimental than a loss of relative internal rotation.

Robotic Arm-Assisted Lateral Unicompartmental Knee Arthroplasty: How Are Components Aligned?

The purpose of this multicenter, retrospective, observational study was to investigate the association between intraoperative component positioning and soft tissue balancing, as reported by robotic technology for a cohort of patients who received robotic arm-assisted lateral unicompartmental knee arthroplasty (UKA) as well as short-term clinical follow-up of these patients. Between 2013 and 2016, 78 patients (79 knees) underwent robotic arm-assisted lateral UKAs at two centers. Pre- and postoperatively, patients were administered the Knee Injury and Osteoarthritis Score (KOOS) and the Forgotten Joint Score-12 (FJS-12). Clinical results were dichotomized based upon KOOS and FJS-12 scores into either excellent or fair outcome, considering excellent KOOS and FJS-12 to be greater than or equal to 90. Intraoperative, postimplantation robotic data relative to computed tomography-based components placement were collected and classified. Following exclusions and loss to follow-up, a total of 74 subjects (75 knees) who received robotic arm-assisted lateral UKAs were taken into account with an average follow-up of 36.3 months (range: 25.0-54.2 months) postoperative. Of these, 66 patients (67 knees) were included in the clinical outcome analysis. All postoperative clinical scores showed significant improvement compared with the preoperative evaluation. No association was reported between three-dimensional component positioning and soft tissue balancing throughout knee range of motion with overall KOOS, KOOS subscales, and FJS-12 scores. Lateral UKA three-dimensional placement does not seem to affect short-term clinical performance. However, precise boundaries for lateral UKA positioning and balancing should be taken into account. Robotic assistance allows surgeons to acquire real-time information regarding implant alignment and soft tissue balancing.