Flexion Alignment Research Articles

Restoring Anatomical Features in Primary Total Knee Arthroplasty.

Today, the number of people affected by gonarthrosis symptoms is increasing proportionally. Total knee arthroplasty (TKA) is a successful intervention that aims to reduce pain and restore knee function. However, studies have shown that active young patients still have limitations in performing activities such as skiing, golfing, surfing, and dancing. Over the last few years, total knee arthroplasty has undergone significant changes. Most of the modern TKA implants are designed to reproduce the normal biomechanics of the knee joint, mimicking the physiological pattern with greater compliance in the medial compartment between the tibial insert and femoral condyle and less congruence on the lateral side. Unfortunately, functional outcomes are compromised in approximately half of TKA patients. This loss may be caused by the abnormal kinematics and inherent instability of many contemporary implants. The proper alignment of the femoral component during TKA is a crucial step that influences postoperative results. The position of the femoral component in the axial plane is responsible for flexion stability, knee joint kinematics, flexion alignment, and patellar tracking. The main goal when choosing a type of prosthesis is to achieve an adequate recovery that leads to an improvement in mobility and an increase in the efficiency of the quadriceps.

A Narrative Review of Patellar Resurfacing Versus Non-resurfacing in Total Knee Arthroplasty.

The number of individuals who experience the symptoms of gonarthrosis rises proportionally as life expectancy rises and the population becomes more active. The purpose of total knee arthroplasty (TKA) is to lessen pain and restore knee function, and it has a high success rate. The restoration of patellar tracking in addition to the proper alignment of the femoral and tibial components contributes to the success of the arthroplasty and the patient's happiness. Replacement of the knee is not an easy process. One of the major objectives of total knee replacement is to achieve the proper rotation of the femoral components. A critical step that affects postoperative outcomes in total knee arthroplasty is the correct alignment of the femoral component. The axial plane of the femoral component is to blame for flexion stability, knee joint kinematics, flexion alignment, and patellar tracking. The patella is the largest sesamoid bone in the human body, and its major role is to enhance the quadriceps' moment arm, which allows the knee to expand. The distribution of patellofemoral compressive pressures during knee flexion and the centralization of the quadriceps muscles' multidirectional pull during extension are both critical functions of the patella. After primary knee arthroplasty, there are 8% more cases of anterior knee discomfort than there were before. Whether or not the patella was resurfaced, patients with primary TKA experience anterior knee discomfort. Patella baja is caused by excessive joint line elevation, which causes persistent overload and discomfort. The design of the TKR might have an impact on postoperative patellofemoral problems. After TKR, patellofemoral maltracking and patellar dislocation are often caused by surgical mistakes.

Limb alignment changes with knee flexion: A study based on CAS data

BackgroundRecent evidence has questioned the value of standing limb alignment for predicting the adduction moment and forces exerted on healthy and prosthetic knees. The purpose of this study was to assess the lower limb alignment of OA knee patients at various knee flexion angles.The main hypothesis was that lower limb alignment measured throughout knee flexion does not significantly differ between patients displaying different extension alignment (neutral, varus or valgus). Methods206 arthritic knee patients undergoing computer-assisted total (CAS) knee prosthesis were included. Frontal limb alignment was assessed in a systematic manner by CAS at three knee positions: extension, 90 degrees of flexion and maximal flexion. The HKA angle at each knee position and the change in HKA angle between two knee positions (delta value) were reported and compared. ResultsA large proportion of OA patients had significant variation in their lower limb alignment (32% with Δ HKA > 5°). The extended limb deformity tended to reduce with knee flexion: mean of 5° and 6° deformity reduction for varus and valgus patients, 40% and 66% of varus and valgus patients progressed to neutral alignment with 90° knee flexion. Forty percent of neutral extended lower limb did not maintain their neutral alignment but rather progressed to either varus or valgus at 90° knee flexion. ConclusionsLimb alignment in extension is a poor predictor of limb alignment in flexion in OA patients.Only considering the traditional frontal alignment of an extended lower limb for planning knee arthroplasty or osteotomy is likely insufficient.

English

The main indication of total knee replacement (TKR) is pain and restricted range of motion of the knee. The key to a successful total knee replacement is correct alignment in flexion and extension. Here we report a case of TKR in severe osteoarthritis (O / A) knee with a large cyst on the medial side of the knee, resulting in the problem of ligament balancing and management with help of an Arthrex Internal brace. Proper diagnosis and treatment plan help to overcome the challenging cases of varus knee. The indication of total knee replacement is pain and restricted range of motion of the knee. Several authors have reported successful outcomes on patient satisfaction in the follow-up of almost ten to fifteen years. 1 Additionally, the results of surgery are satisfactiry with good implant survival. 2 But some patients indeed have poor results and some may require revision surgery in a short duration. The key to a successful total knee replacement is correct alignment and stability in flexion and extension.3 The ligament after balancing of the correctly aligned knee must consider the function of the resected ligaments in flexion and extension, because in TKR both anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are usually sacrificed. In other words, total knee replacement is a soft tissue surgery in which bone is replaced. In the varus knee, medial side structures are tight and compensatory laxity on the lateral side. So knee stability should be managed by the remaining ligamentous structures that are both medial and lateral collateral and capsular ligaments. 4 The gap technique is the gold standard for ligament balancing in total knee replacement. 5 That is the execution of equal medial and lateral gaps as well as balanced flexion and extension gaps. This is usually obtained by medial side release in varus knee as the medial side is contracted and lateral side release in valgus knee accordingly. Here we report a case of TKR in severe osteoarthritis knee with a large cyst on the medial side of the knee, resulting in the problem of ligament balancing and management.

Flexion Dysfunction of Atlanto-Occipital Joint Associated with Cervical Spondylosis.

ObjectiveTo investigate the association between atlanto‐occipital radiographic alignment in flexion and cervical spondylosis (CS).MethodsThis is a retrospective case‐control study. CS patients were recruited from our hospital, and the age/gender/body mass index (BMI)‐matched healthy controls were selected from the subjects in health examinations at the same hospital between January 2015 and May 2019. A total of 464 subjects was included in the study. There are 282 males and 182 females. The ages of patients were 20 to 67 years, and the mean age was 33.9 years. CS patients were considered the case group. Based on surgical treatments, they were subdivided into non‐operation group and operation group. The operation group and non‐operation group had 45 and 187 patients, respectively, while 232 subjects were included in the control group. The angle between McGregor's line and C1 line (O‐C1 angle) was evaluated on images taken in flexion (F‐OC) and neutral positions (N‐OC) independently. The relationship between the FOC (FOC=F‐OC—N‐OC) and Neck Disability Index (NDI) was examined, and the involvement of the FOC in the onset of CS was analyzed. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut‐off for detecting an increased risk of CS.ResultsThe median follow‐up time was 51.6 months (25–115 months). The case groups, especially the operation group, tended to be older (55.8 ± 11.2 vs 41.6 ± 13.8 vs 23.5 ± 5.5 years, P < 0.001), have a higher NDI score (12.2 ± 4.5 vs 6.2 ± 2.1 vs 3.2 ± 1.2, P < 0.001), and longer medical history (10.5 ± 9.5 vs 6.8 ± 11.2 years, P < 0.001). One‐way analysis of variance showed statistically significant differences in FOC between the control and case groups (1.4° ± 1.2° vs 3.6° ± 1.9° vs 7.2° ± 2.0°, P < 0.001). Besides, a post‐hoc Tukey test showed a lower FOC in the operation group compared with that in the non‐operation group (1.4° ± 1.2° vs 3.6° ± 1.9°, P < 0.001). Using FOC as a radiological predictive model to predict CS, the cut‐off value was 4.2°. Using FOC as a radiological predictive model to predict CS, the area under the curve (AUC) was 0.86 (95% CI: 0.78–0.92, P < 0.001). In the univariable risk analysis model, conditional logistic regression showed that the FOC level was an independent factor with an important role in the risk of CS. The odds rose to 8.2 times when FOC reached the level under 4.2° (OR = 8.2; 95% CI: 6.4–10.0; P < 0.001). There existed a significant negative correlation between FOC levels and NDI (r = −0.451, P = 0.016).ConclusionsStiff O‐C1, which is defined as FOC ≤ 4.2°, represented decreased flexion dysfunction of atlanto‐occipital joint and is closely associated with high risk for the occurrence of CS. This finding could show a possible relationship between upper and lower cervical spine and help spine surgeons to understand the pathological process of CS and implement appropriate management.

Optimal Flexion for the Femoral Component in TKR: A Study of Angle Between Mechanical Axis and Distal Anatomic Intramedullary Axis Using 3D Reconstructed CT Scans in 407 Osteoarthritic Knees Studied in India.

The femoral component is generally aligned perpendicularly to the distal femoral intramedullary axis with conventional instruments. Various aids like computer navigation, patient-specific instrumentation and robotic surgery use the mechanical axis as the reference for the femoral component alignment. We studied the flexion of the distal femoral intramedullary axis compared to the mechanical axis using an interactive 3D tool in 407 Indian osteoarthritic knees undergoing total knee replacement to better understand optimal flexion alignment. 407 knees (301-Female, 106-Male) in Indian patients undergoing total knee replacement underwent CT scans. A 3D interactive knee system was used for 3D reconstruction and planning. Distal femoral flexion angle (DFFA) was calculated between the anatomic distal femoral (intramedullary) axis and the mechanical axis. Statistical analysis was performed using ANOVA test and Chi-square test using a data analysis tool pack (Analysis ToolPak by Excel Easy) additionally installed in Microsoft Excel 2010. The mean DFFA was found to be 2.54 with a standard deviation of 1.38. The maximum and minimum values noted were 7.5 and 0.5 respectively. There was no correlation found between sex, age, height or weight (p > 0.05). While taking the distal femur cut with systems other than an intramedullary rod, in Indian osteoarthritic knees, it would be safer to take the distal femoral cut between 2 and 3 degrees of flexion to mechanical axis, as it would ensure that the cut is within 3 degrees from the anatomic axis for 98% patients. Most surgeons routinely using navigation or similar aids take the cut at 0 degrees of flexion to the mechanical axis. This will lead to more than 3 degrees of extension with reference to the intramedullary axis in more than 39% patients. This would result in either an increase in femoral component sizing or an increased risk of notching.

Mechanical alignment changes during flexion in total knee arthroplasty without affecting clinical outcomes

BackgroundPrimary aim of this study is to investigate if Hip-Knee-Ankle angle, measured in the coronal plane, changes with knee flexion after total knee arthroplasty. The secondary aim is to assess the relationship between Hip-Knee-Ankle during knee flexion and clinical outcome at mid-term follow up. Methods334 computer assisted total knee arthroplasties were retrospectively evaluated. A total of 233 patients were available for assessment of clinical outcomes at last follow up (mean 35 months). Hip-Knee-Ankle angle at different degrees of knee flexion and components' alignment were recorded intraoperatively. FindingsPatients were stratified based on the preoperative alignment: 202 varus knees, 99 neutral knees, and 33 valgus knees. In the varus knee group, 146 patients (89%) maintained a neutral overall limb alignment when flexed to 20°, 118 (72%) remained neutrally aligned at 45° and 92 (54%) at 90°. In valgus knee group, 26 (90%) remained neutrally aligned at 20°, 22 (75%) at 45° and 16 (55%) at 90°. In neutrally-aligned knee group, 88 (96%) remained neutrally aligned at 20°, 73 (79%) at 45° and 61 (66%) at 90°. Femoral component external rotation was correlated with varus alignment in flexion. Good outcomes were reported in 181 (78%) cases, fair results in 28 (12%) cases, poor results in 24 (10%) of cases. Poor results were not correlated to Hip-Knee-Ankle angle at different knee flexion angles. InterpretationThis study demonstrates that intraoperative Hip-Knee-Ankle angle changes as the knee moves into deeper flexion. However, neutral Hip-Knee-Ankle through the range of motion does not correlate with superior outcomes.

The effect of flexion alignment in total hip arthroplasty with a cementless tapered-wedge femoral stem.

The influence of stem sagittal alignment on clinical outcomes is unclear in total hip arthroplasty (THA). The purpose of this study is to assess the relationship between stem sagittal alignment and clinical and radiographic outcomes using 3D-CT. We performed 370 consecutive primary THAs between 2009 and 2013. After exclusion, 102 hips in 89 patients using single tapered-wedge stem were included. Mean follow-up was 4.7years. Stem sagittal alignment was measured using CT, and patients were divided into flexion and neutral alignment groups. Clinical and radiographic outcomes were compared between two groups. Furthermore, we evaluated the anterior femoral offset and initial contact state. There were no significant differences in clinical or radiographic outcomes between two groups. CT data analysis and multiple regression analysis showed flexion alignment increased anterior femoral offset (AFO) and Gruen zone 4 contact area. There was no significant difference in clinical or radiographic outcomes between flexion and neutral alignment of the tapered-wedge stem at an average of 4.7years of follow-up. The increase of AFO and distal contact area in flexion alignment could affect the improvement of impingement-free range of flexion and intraoperative fracture.

The Effect of Sagittal Femoral Bowing on the Femoral Component Position in Total Knee Arthroplasty.

In the current study, we investigated that how sagittal femoral bowing can affect the sagittal alignment of the femoral component in total knee arthroplasty (TKA). There were 25 patients underwent TKA. Long leg radiography in lateral view was performed. The sagittal femoral bowing (SFB) and component alignment in relation to the sagittal mechanical axis and distal anterior cortical line (DACL) were measured. Finally, the correlation of component alignment and SFB was examined. Mean SFB was 7±2.7 degrees. The component was in flexion position in relation to mechanical axis and DACL as 8.4±2.9 degrees and 1.7±0.9 degrees, respectively. The flexion alignment of the component was significantly correlated with SFB. Mechanical alignment of the limb in both coronal and sagittal axes should be preserved in TKA. SFB can significantly increased the flexion alignment of the femoral component.

Alignment in knee flexion position during navigation-assisted total knee arthroplasty.

The aim of this study was to demonstrate the lower limb alignment in knee flexion position after navigation-assisted total knee arthroplasty using the gap technique and to identify the correlative factors. One hundred and twenty consecutive osteoarthritic knees (120 patients) were prospectively enrolled for intraoperative data collection. All TKA surgeries were performed using the navigation system (OrthoPilot™, version 4.0; B. Braun Aesculap, Tuttlingen, Germany). Before and after final prosthesis implantation, the lower limb navigation alignment in both knee extension (0°) and knee flexion (90°) position was recorded. The knee flexion alignment was divided into three groups: varus, neutral and valgus alignment. To determine the factors of the alignment in knee flexion position, preoperative demographics, radiologic and intraoperative data were obtained. Pearson's correlation (r) analysis was performed to find the correlation. The Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index were compared between groups. Although all postoperative extension alignment was within neutral position (between -2° and +2°), postoperative knee flexion alignment was divided into three groups: varus (≤-3°), 24 cases (20%); neutral (between -2° and +2°), 85 cases (70.8%) and valgus (≥+3°) alignment, 11 cases (9.2%). There were a good correlation of alignment in knee flexion position with the rotation of femoral component relative to posterior condylar axis (r=-0.502, p=0.000) and weak correlations with posterior femoral cut thickness (lateral condyle) (r=0.207, p=0.026), medial flexion (90°) gap after femoral component rotation adjustment (r=0.276, p=0.003). Other variables did not show correlations. There were no statistical clinical differences between varus, neutral and valgus knee flexion alignment groups. About 30% of the cases showed malalignment of more than 3° in knee flexion position although with neutral alignment in extension position. The knee flexion alignment had a good correlation with the rotation of femoral component relative to posterior condylar axis. Neutral alignment in knee flexion position may be adjusted by femoral component rotation especially by the use of navigation system. IV.

Non-invasive quantification of lower limb mechanical alignment in flexion

Objective: Non-invasive navigation techniques have recently been developed to determine mechanical femorotibial alignment (MFTA) in extension. The primary aim of this study was to evaluate the precision and accuracy of an image-free navigation system with new software designed to provide multiple kinematic measurements of the knee. The secondary aim was to test two types of strap material used to attach optical trackers to the lower limb.Methods: Seventy-two registrations were carried out on 6 intact embalmed cadaveric specimens (mean age: 77.8 ± 12 years). A validated fabric strap, bone screws and novel rubber strap were used to secure the passive tracker baseplate for four full experiments with each knee. The MFTA angle was measured under the conditions of no applied stress, valgus stress, and varus stress. These measurements were carried out at full extension and at 30°, 40°, 50° and 60° of flexion. Intraclass correlation coefficients, repeatability coefficients, and limits of agreement (LOA) were used to convey precision and agreement in measuring MFTA with respect to each of the independent variables, i.e., degree of flexion, applied coronal stress, and method of tracker fixation. Based on the current literature, a repeatability coefficient and LOA of ≤3° were deemed acceptable.Results: The mean fixed flexion for the 6 specimens was 12.8° (range: 6–20°). The mean repeatability coefficient measuring MFTA in extension with screws or fabric strapping of the baseplate was ≤2°, compared to 2.3° using rubber strapping. When flexing the knee, MFTA measurements taken using screws or fabric straps remained precise (repeatability coefficient ≤3°) throughout the tested range of flexion (12.8–60°); however, using rubber straps, the repeatability coefficient was >3° beyond 50° flexion. In general, applying a varus/valgus stress while measuring MFTA decreased precision beyond 40° flexion. Using fabric strapping, excellent repeatability (coefficient ≤2°) was observed until 40° flexion; however, beyond 50° flexion, the repeatability coefficient was >3°. As was the case with precision, agreement between the invasive and non-invasive systems was satisfactory in extension and worsened with flexion. Mean limits of agreement between the invasive and non-invasive system using fabric strapping to assess MFTA were 3° (range: 2.3–3.8°) with no stress applied and 3.9° (range: 2.8–5.2°) with varus and valgus stress. Using rubber strapping, the corresponding values were 4.4° (range: 2.8–8.5°) with no stress applied, 5.5° (range: 3.3–9.0°) with varus stress, and 5.6° (range: 3.3–11.9°) with valgus stress.Discussion: Acceptable precision and accuracy may be possible when measuring knee kinematics in early flexion using a non-invasive system; however, we do not believe passive trackers should be mounted with rubber strapping such as was used in this study. Flexing the knee appears to decrease the precision and accuracy of the system. The functions of this new software using image-free navigation technology have many potential clinical applications, including assessment of bony and soft tissue deformity, pre-operative planning, and post-operative evaluation, as well as in further pure research comparing kinematics of the normal and pathological knee.

Clinical alignment variations in total knee arthroplasty with different navigation methods

BackgroundWe compared the resulting alignment in 90° of flexion and in full extension after total knee arthroplasty (TKA) with two navigation systems using different techniques: a measured resection (MR) system and a gap — balancing (GB) system. MethodsVarus and valgus alignment in extension and flexion was compared in 100 consecutive patients who had TKA with an MR distal–femoral-cut-first technique at one institution and 100 consecutive patients in whom a GB tibial-cut-first technique was used at another institution. Alignment deviation of three degrees or more from neutral was considered an outlier. ResultsNo significant difference between the groups in coronal alignment in extension or flexion was found, but there were three times the number of outliers for clinical alignment in flexion for the MR group compared to the GB group. ConclusionsThe use of the GB tibial-cut-first computer-assisted TKA navigation may provide a more consistent clinical alignment in flexion than systems using an MR technique. Level of evidenceTherapeutic study. Level 2.

No difference in accuracy between pinless and conventional computer-assisted surgery in total knee arthroplasty

Many studies have demonstrated higher precision and better radiological results in Total knee arthroplasty (TKA) with computer-assisted surgery (CAS). On the other hand, studies revealed a lengthening of operation time up to 20 min for this technique and demonstrated rare additional complications as fractures and neurovascular injuries caused by the array pins and any intraoperative array dislocation leads to abortion of CAS. To combine the advantages and eliminate the disadvantages of standard CAS, we evaluated the accuracy of a so-called pinless CT-free version of knee navigation (pinless CAS) abandoning the reference pins and reducing the necessary workflow to a minimum. The present study compares the accuracy of the reference methods of two different CT-free knee navigation software versions (Brainlab Knee 2.1 and Brainlab Knee Express 2.5). Thirty patients received TKA assisted by standard CAS. Intraoperatively, the proposed bony resections of standard CAS were matched with the new pinless CAS. Postoperatively, the results were checked by evaluating the radiographs concerning leg axis, femoral flexion and tibial slope. All results concerning precise cuts (femoral as well as tibial coronal/varus-valgus alignment, femoral flexion alignment and tibial slope, resection height) were comparable between both groups (n.s.). In femoral, we found a mean deviation of coronal alignment of 0.3° (SD 0.7) and flexion of 0.2° (SD 0.8). In tibial, we found a mean deviation of coronal alignment of 0.2° (SD 0.5) and slope of 0.2° (SD 0.6). The mean additional operation time for the pinless CAS was below 2 min. The postoperative mechanical leg axis was within the threshold of 3° in all patients, tibial slope and femoral flexion matched with CAS values. In clinical routine, pinless CAS can comprise the advantages of CAS leaving the disadvantages aside. It reduces surgical time and avoids complications associated with the tracking pins of conventional CAS.

Reliability of leg alignment using the OrthoPilot system depends on knee position: a cadaveric study

Despite the increase in clinical use of navigation systems in total knee arthroplasty, few studies have focused on the reproducibility of these systems. The aim of the present study was to assess the influence of knee position and observer experience on intra- and inter-observer agreement in limb alignment assessment with the OrthoPilot system. Limb alignment in the coronal plane and extension range of the knee were assessed in four embalmed cadaveric specimens by five independent observers and measurements were repeated four times to determine intra- and inter-observer agreement, expressed as intraclass correlation coefficients (ICCs). Additionally, navigation results were compared against figures from conventional measurement of leg alignment (ground truth). Intra- and inter-observer agreements were excellent for assessing the extension range (ICC, 0.97 and 0.95) and the coronal femuro-tibial axis in knee extension (ICC, 0.92 and 0.88) but were generally worse in knee flexion (ICC, 0.62 and 0.55). There was an increased tendency of intraobserver errors in observers with less clinical experience. Mean correlation with conventional measurements was fair (Spearman's rho 0.61). The OrthoPilot system showed excellent reproducibility for assessment of extension range and coronal limb alignment. However, assessments of coronal limb alignment in flexion were prone to error and caution should be taken when relying on these measurements.

Sagittal Alignment of the Cervical Spine After the Laminoplasty

Prospective study. To identify the impact of laminoplasty on range of motion (ROM) and sagittal alignment of the cervical spine. Cervical laminoplasty is an effective procedure decompressing multilevel spinal cord compression. Preoperative lordosis of the cervical spine is a prerequisite for laminoplasty, and maintaining postoperative lordosis is also important for decompression of the spinal cord. Eighty-five patients who planned open door laminoplasty from C3-C7 were studied. Preoperative diagnosis included myelopathy cases associated with cervical spondylosis in 52, ossification of posterior longitudinal ligament in 29, and multilevel disc herniation in 4 cases. Cervical spine lateral radiography in neutral, flexion, and extension were taken before surgery and at 2-year follow-up. The cervical lordosis or kyphosis was measured by the Cobb's method. Diagnosis, degree of preoperative lordosis in the neutral position, and degree of preoperative sagittal alignment in flexion and extension were studied as risk factors for postoperative kyphosis. ROM was decreased 30.5% after laminoplasty. The mean preoperative lordosis in the neutral position was 16.2 degrees and postoperative lordosis was 11.4 degrees. Kyphosis (mean, 12.2 degrees) was observed in 9 patients (10.6%) after surgery. All of them had been diagnosed as myelopathy cases associated with cervical spondylosis. The preoperative lordotic angle was significantly smaller in the kyphotic group than in the lordotic group. In the kyphotic group, preoperative flexion was 10.2 degrees larger and extension was 10.3 degrees smaller than in the lordotic group. The kyphotic group showed 19.3 degrees of kyphosis in flexion and 8.7 degrees of lordosis in extension before surgery. ROM of the cervical spine decreased by 30.5% after laminoplasty. Kyphosis was developed in 10.6% of the patients. The preoperative factors affecting postoperative kyphosis are diagnosis of myelopathy cases associated with cervical spondylosis, a lordosis angle of <10 degrees, and a kyphotic angle during flexion that is larger than a lordotic angle during extension.

Alignment of the femoral component in a mobile-bearing unicompartmental knee arthroplasty: A study in 10 cadaver femora

Use of an intramedullary rod is advised for the alignment of the femoral component of an Oxford phase-III prosthesis. There are users moving toward extramedullary alignment, which is merely an indicator of frustration with accuracy of intramedullary alignment. The results of our study with 10 cadaver femora demonstrate that use of a short and long intramedullary femoral rod may result in excessive flexion alignment error of the femoral component. Understanding of the extramedullary alignment possibility and experience with the visual alignment of the femoral drill guide is essential toward minimizing potential errors in the alignment of the femoral component.

Anterior spinal decompression and fusion for cervical flexion myelopathy in young patients

The mechanism underlying cervical flexion myelopathy (CFM) is unclear. The authors report the results of anterior decompression and fusion (ADF) in terms of neurological status and radiographically documented status in young patients and discuss the pathophysiological mechanism of the entity. Twelve patients underwent ADF in which autogenous iliac bone graft was placed. The fusion area was one segment in four cases, two segments in seven, and three segments in one. Neurological status, as determined by the Japanese Orthopaedic Association (JOA) score, radiographic findings, and intraoperative findings were evaluated. The mean follow-up period was 63.3 months (range 20-180 months). Grip strength was significantly improved and sensory disturbances resolved completely. Intrinsic muscle atrophy, however, persisted in all patients at the final follow-up examination. Local kyphosis in the flexed-neck position at the fusion levels was corrected by surgery. Preoperative computerized tomography myelography revealed that the cord compression index, which was calculated by anteroposterior and transverse diameters of the spinal cord, decreased to 33 +/- 6.2% in the flexed-neck position from 39.7 +/- 9.9% in the extended-neck position. The anterior dura mater-spinal cord distance decreased to 1.9 +/- 0.7 mm in the flexed-neck position from 4 +/- 1.2 mm in extended-neck position. The posterior dura mater-spinal cord distance increased to 2.5 +/- 1.1 mm in the flexed-neck position from 1.3 +/- 0.5 mm in the extended-neck position. Postoperative neurological status was improved in terms of grip strength, sensory disturbance, and JOA score, and local kyphosis in the flexed-neck position at the fusion levels was reduced and stabilized by ADF. In most cases local kyphosis in the flexed-neck position was demonstrated at the corresponding disc level, as were cervical cord compression and decrease of the anterior wall of the dura mater-spinal cord distance in the flexed-neck position. Therefore, the contact pressure between the spinal cord and anterior structures (intact vertebral bodies and intervertebral discs) in the mobile and kyphotic segments was considered to contribute to the onset of CFM. The ADF-related improvement of the clinical symptoms, preventing kyphotic alignment in flexion and decreasing movement of the cervical spine, supports the idea of a contact pressure mechanism. Furthermore, short ADF performed only at the corresponding segments can preserve more mobile segments compared with posterior fusion. Thus, ADF should be the first choice in the treatment of CFM.

Making Your Next Unicompartmental Knee Arthroplasty Last: Three Keys to Success

Alignment, ligament balance, and implant fixation are essential in unicompartmental knee arthroplasty. Adequate exposure allows assessment of the opposite compartment, trimming of medial femoral and tibial osteophytes, and a thorough notchplasty. Intramedullary instruments provide accurate and reproducible alignment of the implants in extension, and the anteroposterior axis offers the best landmark for varus-valgus alignment in flexion and also centers the femoral component on the surface of the tibial component. Complete osteophyte excision frees the collateral and cruciate ligaments and minimizes ligament balancing. The implants should allow 1 to 3 mm of laxity in flexion and extension, and if more laxity is required, reresection should be done posteriorly or distally. Fixation depends on excellent bone stock along with precise alignment, and avoiding tibial overresection ensures adequate support of the implant.

Characteristics of sagittal vertebral alignment in flexion determined by dynamic radiographs of the cervical spine.

This study was conducted to depict the change patterns of intervertebral motion of the cervical spine during flexion, upright, and extension positions using dynamic radiographs. Special interest was focused on the flexion position. To find reliable criteria for judging the normal intervertebral flexibility based on a survey of the normal population. The lateral dynamic radiographs of 75 normal subjects were analyzed by digitization and computer calculation. The characteristics of intervertebral positions were investigated using flexion radiographs. From extension to flexion, the angles of intervertebral angular displacement changed from lordosis with different degrees to nearly 0 degrees, which means the adjacent endplates are almost parallel, except at C1-C2; the intervertebral translation changes from slightly retrolisthetic to zero displacement. Using C2-C3 as a baseline to calculate the intervertebral differences of angular displacement and translation in flexion radiographs, nearly all the intervertebral differences of angular displacement were less than 7 degrees, and those of translation were less than 0.06 mm. Qualitative changes from extension to flexion and quantitative values of intervertebral differences in flexion radiographs help define the normal flexibility of the cervical spine more accurately.