全膝关节置换术两种入路效果比较

 目的  比较经股内侧肌入路与内侧髌旁入路行全膝关节置换术的临床疗效。 方法 25例行同期双侧全膝关节置换术,每例患者随机一侧采用经股内侧肌入路,另一侧采用内侧髌旁入路,观察两组手术时间、术后引流量、术后6周关节活动度、直腿抬高恢复时间,术后第1、2、3、6天对每例患者双侧膝关节进行视觉模拟疼痛评分（visual analog scale,VAS）。 结果 经股内侧肌入路组在直腿抬高恢复时间［（2.2±0.8） d vs （4.4±1.4）d］、VAS评分方面明显优于内侧髌旁入路组( P <0．05 ),两组在术后引流量、手术时间、术后6周膝关节活动度方面差异无统计学意义( P >0．05)。 结论 经股内侧肌入路行全膝关节置换术与髌旁入路相比,可以减轻术后的疼痛,减少直腿抬高恢复时间,较早恢复膝关节功能,值得临床推广和应用。     

TKA using the subvastus approach and lateral retinacular release in patients with permanent post-traumatic patellar dislocation: a report of two cases

Permanent post-traumatic patellar dislocation is a rare condition, and total knee arthroplasty (TKA) can be performed for osteoarthritic knees with this condition. There have been only a few reports about using the standard medial parapatellar approach and extensive lateral release or extensor mechanism realignment for patients with permanent post-traumatic patellar dislocation. We performed two TKAs with using a subvastus approach and lateral release for osteoarthritic knees with permanent post-traumatic patellar dislocation. The patients were well satisfied with their results. The patellae tracked very well in the femoral trochlear groove throughout the full range of motion after the operations. Bone scans were done 1 year postoperatively on both patients, and the scans showed normal vascularity for the patella.     

Diagnosis and treatment of patients with patellofemoral pain

The patient-athlete with patellofemoral pain requires precise physical examination based on a thorough history. The nature of injury and specific physical findings, including detailed examination of the retinacular structure around the patella, will most accurately pinpoint the specific source of anterior knee pain or instability. Radiographs should include a standard 30 degrees to 45 degrees axial view of the patellae and a precise lateral radiograph. Nonoperative treatment is effective in most patients. Prone quadriceps muscle stretches, balanced strengthening, proprioceptive training, hip external rotator strengthening, patellar taping, orthotic devices, and effective bracing will help most patients avoid surgery. When surgery becomes necessary, indications must be specific. Lateral release is appropriate for patella tilt (abnormal rotation). Painful scar or retinaculum, neuromas, and pathologic plicae may require resection. Proximal patellar realignment may be accomplished using arthroscopic or a combined arthroscopic/mini-open approach. Symptomatic articular lesions and more profound malalignments may require medial or anteromedial tibial tubercle transfer. Clinicians should be particularly alert for symptoms of medial subluxation in postoperative patients and should use the provocative medial subluxation test followed by lateral displacement patellar bracing to confirm a diagnosis of medial patellar subluxation. This problem may be corrected in most patients using a lateral patellar tenodesis. Current thinking emphasizes precise diagnosis, rehabilitation involving the entire kinetic chain, restoration of patella homeostasis, minimal surgical intervention, and precise indications for more definitive corrective surgery.     

Midvastus approach in total knee arthroplasty: a randomized, double-blinded study on early rehabilitation

The medial parapatellar approach has become the standard technique in total knee arthroplasty (TKA). However, recent studies have reported superior results regarding functional recovery when using the midvastus approach. It was the aim of this study to evaluate the early functional outcome of both surgical techniques. In a prospective, double-blinded, randomized study, 50 patients for TKA were consecutively operated on either by the medial parapatellar or the midvastus approach. Exclusion criteria were defined as previous open knee surgery and leg deformity of more than 10° varus or valgus. TKA was performed in all patients by one surgeon using the same type of implants in both groups. Pain scores (VAS) were documented and follow-up data including quadriceps strength and proprioception were obtained 3 weeks and 6 weeks postoperatively. Both groups were comparable in preoperative demographic data. Postoperatively, patients in the midvastus group demonstrated significantly lower pain in rest (VAS: mean 2.25 vs. 3.03) and under movement (VAS: mean 2.92 vs. 3.13). Further, they showed superior isometric quadriceps strength at 3 weeks (41.4 vs. 27.6 Nm) and 6 weeks (47.6 vs. 35.5 Nm). Moreover, this group showed a superior postoperative proprioception, while the range of motion was similar in both groups. The midvastus approach offers advantages over the standard parapatellar arthrotomy, in the early rehabilitation period. No adverse effects were observed associated with this approach. Therefore, the midvastus approach should be considered as a valuable alternative in TKA.     

Effects of four different surgical approaches on intra-operative joint gap in posterior-stabilized total knee arthroplasty

Purpose

The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear. We hypothesized that joint gap changes with different knee flexion angles would not be consistent within four different approaches and two different patellar positions.

Methods

This study enrolled 80 knees undergoing posterior-stabilized TKA. For 60 varus knees, parapatellar, midvastus, and subvastus approaches were used in 20 knees each. For 20 valgus knees, a lateral subvastus approach was used. Component gap length and inclination were measured intra-operatively using a specific tensor device under 40 lb with the patella reduced or shifted laterally, at 0°, 45°, 90°, and 135° of knee flexion.

Results

Mean gap lengths at 45° and 90° of knee flexion were significantly larger with the parapatellar approach than with midvastus or lateral subvastus approaches (P < 0.05). Regarding gap inclination, varus angle increased linearly through the entire arc of flexion in all four approaches. When the patella was shifted laterally, gap lengths at 45°, 90°, and 135° were significantly reduced compared with those for the patella reduced in the subvastus approach, whereas gap length was constant in the parapatellar approach, regardless of patellar position.

Conclusion

Joint gap kinematics was not consistent within four different approaches and two different patellar positions. Relatively large gaps at 45° and 90° were unique features for the parapatellar approach. Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.

Level of evidence

II.     

Effect of taping the patella on concentric and eccentric torque and EMG of knee extensor and flexor muscles in patients with patellofemoral pain syndrome

The acute effect of patella taping on torque and electromyographic (EMG) activity in maximal voluntary concentric and eccentric action of the knee extensor and flexor muscles in patients with patellofemoral pain syndrome was studied in 48 patients (62 knees). The patients (28 female, 20 male) were tested concentrically and eccentrically on a Kin-Com dynamometer with simultaneous EMG recording with the patella untaped and medially or laterally taped. Patients with clinically normal patellar mobility did not improve their quadriceps performance by taping of the patella: after medial taping they decreased theur muscle torque during concentric work at 60°/s (P<0.05) and eccentric work at 180°/s (P<0.05). After lateral taping they decreased their muscle torque during concentric work at 60°/s (P<0.01), and 180°/s (P<0.05) and eccentric work at both 60°/s (P< 0.01) and 180°/s (P< 0.05). Moreover, these patients also decreased their agonist EMG activity during concentric work at 60°/s (P<0.05) and 180°/s (P<0.05) and their antagonist EMG activity during eccentric work at 60°/s (P<0.01). Patients with a clinical lateral patellar hypermobility increased their knee extensor torque after medial taping at 60°/s during both eccentric work (P<0.01) and concentric work (P<0.05). The greatest improvement in quadriceps performance, however, was in patients with a clinical medial patellar hypermobility. They increased their knee extensor torque after lateral taping during eccentric work at both 60°/s (P<0.001) and 180°/s (P<0.001) and during concentric work at 60°/s (P<0.001). They also increased agonist EMG activity during eccentric work at both 60°/s (P<0.01) and 180°/s (P<0.001) and during concentric work at 180°/s (P<0.05). Patients with both lateral and medial patellar hypermobility increased their knee extensor torque by patellar taping in either direction; after medial taping there was an increase during eccentric work at both 60°/s (P<0.01) and 180°/s (P<0.05) and after lateral taping they also showed an increase during eccentric work at 60°/s (P<0.01). There was a slight decrease in knee flexor torque with either medial or lateral taping in comparison with no taping. Furthermore, there was higher antagonist EMG activity during hamstring measurements when the patella was either medially or laterally taped as opposed to untaped. In all four groups of patients, except for the group with lateral and medial hypermobility, there was a highly significant correlation between patients' own evaluation of the taping and their patellar mobility according to the clinical examination.This study was supported by grants from the Swedish Sports Federation and from Beiersdorf Compancy, Homburg, Germany     

Modified Elmslie-Trillat procedure for instability of the patella

The purpose of this study was to determine whether or not the modified medial transfer of the ligamentum patellae in case of objective instability of the patella is an adequate therapy and if it is possible to improve the patellar congruence angle by this method. Between October 1987 and April 1993, 41 operations were performed in 37 patients with medialization of the medial third of the ligamentum patellae with the corresponding part of the tibial tubercule. Four patients needed a bilateral operation; the two interventions were not performed at the same time. Thirty-six operated knees (88%) were examined at a median clinical and radiological follow-up of 62.8 months (± 15.8 SD). For evaluation, the objective and subjective Turba score was used, and pre- and postoperative X-rays were compared. The patients’ average age at the time of intervention was 23.2 years (± 7 years SD). The operation was performed 39 times for recurrent dislocation or subluxation, for patella alta with cartilage tissue damage, and for first time traumatic dislocation. The only postoperative complication was a temporary peroneal paresis. There were no redislocations seen at the follow-up. One patient with repeated subluxations underwent an additional lateral release combined with a repair of the medial retinaculum. In all other cases, the Turba score showed good or excellent results (subjective 1.9; objective 0.8), the patellar congruence angle was significantly improved (P < 0.001), and there were no medial subluxations. We conclude that the transfer of the medial third of the ligamentum patellae for objective instability of the patella is a minimally invasive and adequate technique to improve significantly a pathological patellar congruence angle.     

Clinical and radiological outcome of medial patellofemoral ligament reconstruction with a semitendinosus autograft for patella instability

Background: Recurrent patellar instability is a common problem after dislocation. The medial patellofemoral ligament (MPFL) contributes 40–80% of the total medial restraining forces. This study assessed the clinical and radiological outcome after a follow-up of 4 years after linear MPFL reconstruction using an ipsilateral Semitendinosus tendon autograft. Study design and methods: 15 knees in 12 patients were examined with a mean of 47 months after linear reconstruction of the MPFL at a mean age of 30 years. 3 knees underwent previous surgery. 3 patients had mild trochlear dysplasia grade I or II, according to the classification of Dejour. If preoperative tibial tuberosity-trochlear groove distance (TTTG) was more than 15 mm, patients underwent additional medialisation of the tibial tuberosity (n=8) creating a similar postoperative situation for all patients. All patients were available for a postoperative evaluation, which consisted of a subjective questionnaire, the Kujala score, and the recording of potential patellar redislocation and apprehension. Patellar height and tilt was measured on plain radiographs. Postoperative CT scans were performed in patients with an additional tibial tuberosity-transfer. Results: Postoperatively, one patient reported on recurrent bilateral redislocation. Physical examination however revealed no findings. Three knees presented with persistent patellar apprehension. Thirteen knees had improved subjectively after surgery. The mean Kujala score improved significantly from 55.0 to 85.7 points. The patellar tilt decreased significantly from 11.3° to 9.2°. Four knees had patella alta preoperatively, but only two at the latest follow-up visit. Previous surgery or additional trochlear dysplasia had no influence on the clinical outcome. Conclusion: MPFL reconstruction improves clinical symptoms, reduces the patellar tilt substantially, and may correct patella alta. Additional mild trochlear dysplasia did not compromise the outcome; however, this fact needs further attention in a larger study group.     

Axial and lateral radiographs in evaluating patellofemoral malalignment.

This is a prospective study of 431 patients (862 knees) with patellofemoral pain, patellar dislocation, or other abnormalities of the knee joint. There were 217 asymptomatic knees with no contralateral problems for comparison. All patients had a history and physical and radiographic examination of both knees. The radiographs included standard anteroposterior views, axial views at 30 degrees of knee flexion, and standing lateral views at 0 degree and 30 degrees of flexion. The presence of patellar tilt or subluxation was noted on the axial view. The lateral view of the patella, with precise overlap of the posterior femoral condyles, allowed determination of relationships between the patella's medial edge, median ridge, and lateral edge to assess patellar tilt. Sixty-two percent of patients with patellar dislocations demonstrated subluxation on the axial view, while 98% demonstrated an abnormal lateral view. Eighteen percent of the control knees revealed evidence of subluxation on the axial view while 35% demonstrated subluxation on the extended lateral view. The axial view demonstrated 62% sensitivity for dislocation, while the lateral view taken in full extension demonstrated 98% sensitivity. The specificity for previous dislocation was 82% for the axial view and 93% for the lateral flexed view. Given the high sensitivity of the lateral view for detecting prior patellar dislocation, a normal result on this view can virtually eliminate the question of previous dislocation. Also, with the high specificity of the axial view and lateral view with knee flexion, the two views combined can confirm a clinical impression of patellofemoral malalignment.     

Kinematic and dynamic axial computed tomography of the patello-femoral joint in patients with anterior knee pain

Thirty-eight knees of 26 patients with anterior knee pain (12 bilateral) were included in the study. There were 22 women and 4 men, and their average age was 29 years. Axial computed tomography (CT) examination of both knees were done at 0°, 10°, 20°, 30°, 40° and 60° of flexion with and without muscle contraction. Images were always taken at the mid-patellar level. Patellar tilt angle (PTA), congruence angle (CA) and sulcus angle (SA) were measured at each knee position. Normal values were also obtained from 14 healthy volunteers (28 knees). Thus, the types of patello-femoral incongruence were determined at each knee position: 1, tilt+lateralisation (TL: 12 knees); 2, lateralisation (L: 4 knees); 3, medialisation (M: 5 knees); 4, lateral to medial instability (LM: 1 knee); 5, tilt (T: 1 knee). Fifteen knees were classified as normal. When the groups were analysed separately, in the TL group the T or L component would have been missed in nine cases if the images were taken only at 30° or only in the first 30° of flexion. In the L group two patellae were reduced at 30°. In three knees in the M group, medialisation began at 10°, 20° and 30°. One patella was reduced at 40°. In the LM case, the patella was lateralised at 0°, 10°, 20° and medialised at 30° and 40°. In the T case, the patella was tilted only at 20°, 40° and 60°. This study showed that axial images taken only at 30° will miss important information. Imaging in the first 30° of flexion will not reveal the correct type of instability, either. Serial imaging over a wider range of flexion is necessary for the correct diagnosis. Determination of the type of incongruence at different knee positions is a new concept. With this methodology, the presence of medial and lateral to medial instabilities is verified. Hence, the classification systems including only lateral instability should be questioned.     

In vivo and noninvasive three-dimensional patellar tracking induced by individual heads of quadriceps

PURPOSE: Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components. METHODS: Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements. RESULTS: Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella. CONCLUSIONS: The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.     

The effect of patellar thickness changes on patellar tilt in total knee arthroplasty

We hypothesized that changes in patellar thickness following patellar resurfacing affect patellar tilt in total knee arthroplasty (TKA) patients. The study enrolled 272 TKAs and categorized them into four groups according to change in patellar thickness: (A) thinner by 1 mm or more, (B) equal or thinner by less than 1 mm, (C) thicker by 1 mm or less, and (D) thicker by more than 1 mm. Patellar tilt angle was measured postoperatively using Merchant radiography. There were no significant differences in postoperative patellar tilt among groups A, B, and C (n.s). However, the postoperative patellar tilting angle of group D was significantly higher than that of all other groups (P < 0.05). Postoperative patellar tilt increased when the postoperative patella was >1 mm thicker than the preoperative patella.     

Patellar tracking abnormalities: clinical experience with kinematic MR imaging in 130 patients

A kinematic magnetic resonance (MR) imaging technique for assessment of malalignment of the patella, involving the acquisition of multiple sequential axial images of the patellofemoral joint during the early increments of passive knee flexion, was used to evaluate 130 patients (235 symptomatic patellofemoral joints) showing clinical evidence of having patellar tracking abnormalities. Twenty-three of the patellofemoral joints had undergone previous surgical procedures for patellar realignment. In addition, 14 (28 patellofemoral joints) asymptomatic control subjects were studied. Normal patellar tracking was observed in all of the asymptomatic subjects and in 43 (17%) of the 260 patellofemoral joints in the patient population, 18 (7%) of which were symptomatic. Sixty-nine (26%) of the patellofemoral joints had lateral subluxation of the patella, 106 (41%) had medial subluxation of the patella, 21 (8%) had excessive lateral pressure syndrome, 19 (7%) had lateral-to-medial subluxation of the patella, and two (1%) had dislocation of the patella. Of the 235 patellofemoral joints with suspected abnormalities, 217 (93%) had patellar malalignment. Of the 23 patellofemoral joints that had undergone prior surgery, 20 (87%) had abnormal patellar tracking. Thirteen of 14 (93%) patellofemoral joints that had undergone a prior arthroscopic lateral retinacular release had a medially displaced patella.     

髌骨倾斜导致髌骨软骨软化实验研究

为了研究髌骨倾斜是否为髌骨软骨软化（ＣＰ）的病因,髌骨软骨软化的发生与何种异常应力有关,选用２４只雌性新西兰兔,随机分４组,每组６只。右膝为实验侧,将髌外侧支持带紧缩造成髌骨外侧倾斜,左膝实施假手术为对照侧,定期处死动物,分别进行髌骨倾斜角Ｘ线测量、髌骨软骨面的接触压力测量、软骨组织切片观察以及软骨组织Ｍａｎｋｉｎ评分。结果显示：实验侧髌骨倾斜角明显大于对照侧。术后６周至１２周时,实验侧髌骨内侧软骨面接触压力明显较对照侧减低（ｐ＜０．０５）。光镜下,术后６周时髌骨内侧面软骨中层与深层轻度变性,１２周至１８周时软骨明显变性,软骨细胞坏死或Ｃｌｏｎｅ状增生,中层与深层软骨基质较多纵行裂隙以及片状苏木素深染的纤维网,表面溃疡形成,ＳａｆｒａｎｉｎＯ染色提示蛋白多糖严重丢失。软骨组织Ｍａｎｋｉｎ评分,实验侧髌骨内侧面软骨得分高于髌骨外侧面软骨（ｐ＜０．０５）,说明髌骨内侧面软骨退变较外侧面明显。结论：髌骨倾斜造成髌骨内侧面应力减低导致髌骨软骨软化。     

Kinematic and dynamic axial computerized tomography of the normal patellofemoral joint

Fourteen normal volunteers with no history suggesting previous or current knee pathology underwent axial computed tomographic examination of the patellofemoral joint. There were 11 men and 3 women, whose ages ranged from 10 to 46 years (average 25 years). Axial images were obtained at 0°, 10°, 20°, 30°, 40°, and 60° flexion both with and without contraction of the thigh muscles. Thus, 12 images were obtained for each individual. The CT scanner was focused at the midpatellar level prior to each image. Three measurements were made on 24 knees for each individual: congruence angle (CA), patellar tilt angle (PTA), and sulcus angle (SA). PTA increased slightly from 0° to 20°, and decreased slightly with more flexion (not significant, NS). The lower limit of PTA was usually 9°–10°: it was not lower than 7° in any knee position. Muscle contraction increased PTA slightly at each degree of flexion (NS). Mean CA was +18.3° (SD 20.8°) at 0°, which means that normal individuals may have CAs as high as +39° at full extension. There was a gradual decrease in CAs with knee flexion. The mean values became negative between 20° and 60° flexion. Contraction of the thigh muscles caused lateralisation of the patella except at 30° and 40° flexion. This lateral pull was statistically significant at full extension (P<0.01) and at 10° flexion (P<0.05). The SA decreased gradually as the flexion of the knee increased. Angles at 0°, 10°, and 20° flexion were significantly higher than those at 40° and 60° flexion (P<0.05). This study shows that CA, PTA and SA change depending on the degree of flexion of the knee, and that these angles show wide variations in the normal population. One should not rely on axial images taken at full extension, as this may erroneously lead to a diagnosis of subluxation in a normally tracking patella. The values obtained in this study may provide a basis for determining the type of patellar instability at different knee positions, and thus give a better profile or patellar tracking. This is a new concept. Besides, comparison of dynamic values obtained in this study with the ones in abnormal patellofemoral joints may also reveal useful information.     

Avoidance of patellar eversion improves range of motion after total knee replacement: a prospective randomized study

Minimally invasive surgery has recently been introduced in TKA surgery. The purpose of this study was to evaluate the effect of eversion of the patella, on safety and functional result after TKA. In a prospective, randomised, double blinded trial, 60 patients were divided in two groups: group A underwent TKA through a standard medial parapatellar arthrotomy, with patellar eversion. Group B underwent the same exposure, except for the fact that the patella was subluxed laterally. All other treatment protocols were identical. Outcomes were measured until 1 year postoperatively. Radiographic evaluation included AP, lateral, skyline and full leg standing radiographs. VAS, WOMAC score, Knee Society Knee and Function score were performed. Active and passive range of motion (ROM) and knee proprioception was measured. All patients underwent isokinetic strength testing. The mean passive ROM changed from 121° preoperatively to 121° postoperatively in group A, compared to 118°–131° respectively in group B at 1 year (P = 0.003). The mean active ROM changed from 112° to 115° in group A, and from 108° to 125° in group B (P = 0.005). All other parameters were not significantly different. Patellar dislocation without eversion for exposing the knee during TKA is a safe procedure and improves ROM at 1 year postoperatively.     

Evaluation of patellar tracking in symptomatic and asymptomatic individuals by magnetic resonance imaging

Objective To determine the patterns of patellar motion in subjects without knee symptoms using dynamic magnetic resonance imaging (MRI).Design Patellar tracking MR examinations were performed on 50 asymptomatic volunteers. The presence and degree of lateral subluxation and tilt of the patella was assessed independently by three radiologists, and discrepancies resolved by consensus. Using the same criteria, the tracking pattern in 50 consecutive patients, recently referred for imaging assessment of anterior knee pain, was studied.Patients Fifty volunteers (22 male, mean age 37 years) and 50 unmatched patients (15 male, mean age 25.5 years) were examined.Results and conclusions Forty-one per cent of a total of 97 knees in the volunteer group showed evidence of lateral subluxation, which was either minimal (grade 1, 32%) or minor (grade 2, 9%). No volunteer demonstrated major (grade 3) subluxation; lateral tilt without translation of the patella was also seen (2%). In the patient group, higher grades of lateral subluxation were more common. Minimal (grade 1) lateralization is a common movement pattern of the patella on knee extension, and should be regarded as normal.     

Magnetic resonance imaging of patellofemoral relationships

Patellofemoral relationships were analyzed in 11 patients (13 knees) with patellar dislocation and 15 asymptomatic subjects (15 knees) at 0° and 20° of flexion. The measurements were made from five consecutive axial images through the patellofemoral joint. The six indices measured were lateral patellar tilt (LPT), lateral patellofemoral angle (LPA), lateral patellar displacement (LPD), patella-lateral condyle index (L/PW), congruence angle (CA), and sulcus angle (SA). The reproducibility of the method was evaluated. The difference between the two study groups was more evident at 0° than at 20° of knee flexion. Significant differences were noted between measurements made at different levels of the joint, particularly in the controls. Isometric contraction of the quadriceps muscle lateralized and tilted the patella slightly in both groups. L/PW with and without quadriceps muscle contraction, and LPA with reference to the anterior condyles differentiated between the two study groups most clearly. LPT and LPA with reference to the anterior condyles differentiated the study groups better than LPT and LPA with reference to the posterior condyles. The reproducibility was good except for inter-observer comparison of CA and SA. The use of an imaging plane selected at the midpoint of the patellar articular cartilage increases the sensitivity of the measurements, since it takes into account both the height of the patella and the tendency towards lateralization. These results indicate that patellar tilt is best measured with the LPA index and patellar lateralization with the L/PW index at 0° knee flexion. This study should always include isometric contraction of the quadriceps muscle.     

Locked lateral patellar dislocation: a rare case of irreducible patellar dislocation requiring open reduction

Irreducible patellar dislocations are rare injuries, but those that do occur are mainly directed intra-articularly. In this case, a 53-year-old woman sustained a locked lateral patellar dislocation when falling from a chair. A preoperative CT-scan revealed bony avulsions at the insertion of the vastus medialis muscle, the medial retinaculum, and partial disruption of the ligamentum patellae from the apex patellae. Open reduction was necessary and the torn structures were reattached with anchor systems and sutures. Postoperative management included intensive physiotherapy. At 1 year after surgery, the patient was without swelling or pain and had a normal gait, but flexion was restricted to 120°. All postoperative radiographs showed the patella correctly placed in the femoral groove. Received: 21 December 1998 Accepted: 15 April 1999     

Patellofemoral Instability in Children: Imaging Findings and Therapeutic Approaches

Patellofemoral instability (PFI) is common in pediatric knee injuries. PFI results from loss of balance in the dynamic relationship of the patella in the femoral trochlear groove. Patellar lateral dislocation, which is at the extreme of the PFI, results from medial stabilizer injury and leads to the patella hitting the lateral femoral condyle. Multiple contributing factors to PFI have been described, including anatomical variants and altered biomechanics. Femoral condyle dysplasia is a major risk factor for PFI. Medial stabilizer injury contributes to PFI by creating an imbalance in dynamic vectors of the patella. Increased Q angle, femoral anteversion, and lateral insertion of the patellar tendon are additional contributing factors that affect dynamic vectors on the patella. An imbalance in the dynamics results in patellofemoral malalignment, which can be recognized by the presence of patella alta, patellar lateral tilt, and lateral subluxation. Dynamic cross-sectional images are useful for in vivo tracking of the patella in patients with PFI. Therapeutic approaches aim to restore normal patellofemoral dynamics and prevent persistent PFI. In this article, the imaging findings of PFI, including risk factors and characteristic findings of acute lateral patellar dislocation, are reviewed. Non-surgical and surgical approaches to PFI in pediatric patients are discussed.