Shortening of patellar tendon after total knee arthroplasty (TKA) was previously reported by several studies. Its etiology still remains controversial. Patellar tendon shortening, a direct cause of patella baja, has a dramatic negative impact in terms of clinical outcomes after TKA. Main objective of this study is to assess the feasibility of utilizing a different technique with Ultrasound that is easy to use, cost-effective and able to eliminate the problem of differential magnification occurring in other techniques which count on standard x-rays and to establish the correlation between clinical outcomes and changes in patellar tendon length and thickness after TKA. The study was designed as prospective cohort and, after a minimum of 4-year-follow up period, 47 knees of 24 patients who had undergone primary TKA without patellar resurfacing were included in the study. All patients were scored with Kujala and HSS scores and all patellar tendons were evaluated with USG regarding their length and thickness. We used conventional grey-scale ultrasound imaging (US) to determine any changes in patellar tendon morphology. All cases were evaluated by the same radiologist. The patellar tendon was examined with the knee in 30° flexion. The flexion angle helped to stretch the extensor mechanism and avoid anisotropy (concavity) of the patellar tendon. The transducer was placed along the long axis of the tendon. The patellar tendon was initially examined in the longitudinal plane in order to measure the total length. Then, total length was divided into three parts and sagittal thickness was calculated at the proximal, median, and distal thirds of the patellar tendon. Both the length and thickness of the tendon were measured before surgery and at the 4th year of follow-up. Of the 47 knees that were included in our study, the mean pre-operative and postoperative length of the patellar tendon was 40.78±6.15 mm and 35.93±4.52 mm. Our results suggested significant shortening of the patellar tendon after primary TKA surgery (p<0.05). Intergroup analysis suggested that reduced sagittal thickness in the proximal third of the tendon was more strongly correlated with an increase in functional outcomes (p<0.05). Our results suggested no significant difference in clinical outcome scores between patients with increased or decreased length of the patellar tendon after TKA (p>0.05). We suggest that determining morphologic changes in sagittal thickness as well as length is important in explaining some of the ambiguous causes of anterior knee pain and impaired clinical outcomes after TKA. More accurate documentation of morphologic changes in the patellar tendon after TKA will certainly help to develop new techniques by surgeons or avoid some existing routines that may harm the tendon. USG is a feasible method for evaluating patellar tendon morphology after TKA but more future studies are needed

An understanding of the remodelling of tendon is crucial for the development of scientific methods of treatment and rehabilitation. This study tested the hypothesis that tendon adapts structurally in response to changes in functional loading. A novel model allowed manipulation of the mechanical environment of the patellar tendon in the presence of normal joint movement via the application of an adjustable external fixator mechanism between the patella and the tibia in sheep, while avoiding exposure of the patellar tendon itself. Stress shielding caused a significant reduction in the structural and material properties of stiffness (79%), ultimate load (69%), energy absorbed (61%), elastic modulus (76%) and ultimate stress (72%) of the tendon compared with controls. Compared with the material properties the structural properties exhibited better recovery after re-stressing with stiffness 97%, ultimate load 92%, energy absorbed 96%, elastic modulus 79% and ultimate stress 80%. The cross-sectional area of the re-stressed tendons was significantly greater than that of stress-shielded tendons. The remodelling phenomena exhibited in this study are consistent with a putative feedback mechanism under strain control. This study provides a basis from which to explore the interactions of tendon remodelling and mechanical environment

Introduction: Patellar tendon is one of the main donor sites for graft. Postoperatively, during the healing procedure there are changes, which we recorded and combined them with the clinical image respectively. Material and Methods: During the period 1998–2001 in Sports Injury Unit, we operated for Anterior Cruciate Ligament insufficiency with autologous Bone Patellar Tendon Bone (BPTB) graft 265 patients. We used autologous BPTB graft from the middle third. We got near the two parts after taking the graft and we sewed very well the peritendon fascia. All patients, with few differentiations, followed the same rehabilitation program. Seventy -seven of them (44 men and 33 women ranging from 17 to 44 years -mean: 24,3 years), were imaged postoperative with MRI at specific intervals from the operation between 3–36 months. In the same time we checked the patients clinically. Results: No one study can answer which is the exact time of satisfying or complete healing. Our study shows elements of scar tissue in the middle third of patellar tendon which is decreasing given time. After the 12th month, the proportion between healthy and scar tissue changes and healthy tissue become dominant. But in some cases scar is still existing even after 36 months. The clinical problems such as anterior knee pain are not existed after the 8th postoperative month. Conclusion: In conclusion, we can say that “regeneration” and healing of patellar tendon occurs mainly during the first postoperative year, but it doesn’t stop after this time. So, we couldn’t recommend this donor site for revision reconstruction before the completion of one year postoperatively

We compared the biological characteristics of extrinsic fibroblasts infiltrating the patellar tendon with those of normal, intrinsic fibroblasts in the normal tendon in vitro. Infiltrative fibroblasts were isolated from the patellar tendons of rabbits six weeks after an in situ freeze-thaw treatment which killed the intrinsic fibroblasts. These intrinsic cells were also isolated from the patellar tendons of rabbits which had not been so treated. Proliferation and invasive migration into the patellar tendon was significantly slower for infiltrative fibroblasts than for normal tendon fibroblasts. Flow-cytometric analysis indicated that expression of α5β1 integrin at the cell surface was significantly lower in infiltrative fibroblasts than in normal tendon fibroblasts. The findings suggest that cellular proliferation and invasive migration of fibroblasts into the patellar tendon after necrosis are inferior to those of the normal fibroblasts. The inferior intrinsic properties of infiltrative fibroblasts may contribute to a slow remodelling process in the grafted tendon after ligament reconstruction

Introduction: Anterior cruciate ligament (ACL) rupture impairs knee stability. Reconstruction of the ACL is therefore performed to restore knee stability and avert risk of subsequent ligament and meniscal injury. Bone-patellar tendon-bone autograft is the most commonly employed technique for ACL reconstruction and considered the “gold standard”. Although 10% postoperative patellar tendon shortening has been reported with this technique, there are no systematic studies assessing the effect of this shortening on patellofemoral joint (PFJ) biomechanics under loading conditions simulating normal physiologic activity. The purpose of this study was to determine if 10% shortening of the patellar tendon affected PFJ biomechanics. Methods: Patellofemoral contact characteristics were evaluated in cadaveric knees before and after patellar tendon shortening. Tendon shortening was performed using a specifically designed device that shortened the tendon without interfering with its anatomic and physiologic integrity. Conditions simulating light physical activity such as level walking were recreated by applying physiological quadriceps loads and corresponding angles of tibial rotation to the PFJ at 15°, 30° and 60° of knee flexion. PFJ contact areas were measured at each position of knee flexion before and after patellar tendon shortening using the silicone oil-carbon black powder suspension squeeze technique (3S technique, . Yao & Seedhom, . Proc Instn Mech Engrs. 1991. ;. 205. :. 69. –72. ). Differences were compared using the Wilcoxon signed rank t-test, with p< 0.05 required for statistical significance. Results: Twelve unembalmed cadaveric knees (median age 81.8 years, 8 female: 4 male) were available for study. Five knees had evidence of osteoarthritic changes, and were rejected. The remaining 7 knees were macroscopically intact and were considered adequate for the experimental procedure. The mean patellofemoral contact areas and stresses determined preoperatively were comparable to those reported in normal knees in previous studies. Following patellar tendon shortening, PFJ contact areas were displaced superiorly on the patellar articular surface and distally on the femoral articular surface. Although the PFJ contact area increased by 17% at 15° of knee flexion (p=0.04), no significant change occurred at 30° or 60° of knee flexion (p> 0.05). Patellofemoral contact stress did not differ before and after patellar tendon shortening (p> 0.05) at any angle of knee flexion. Conclusions: Our results suggest that with light activity such as level walking, a 10% postoperative shortening of the patellar tendon does not alter patellar tracking (in particular contact stresses) and therefore may not impact biomechanics of the patellofemoral joint. Extrapolating these results to the clinical scenario, deleterious consequences on the patellofemoral joint are unlikely after bone-patellar tendon-bone autograft reconstruction of the ACL despite the possibility of postoperative patellar tendon shortening

Introduction: Patients with neglected patellar tendon ruptures present with weakness, instability, extensor lag and sometimes pain. Reports in the literature describe autograft and allograft reconstruction and sometimes quadricepsplasty. Post-operative splintage with a cast or brace is often recommended. Aim: To describe a simple effective method of surgical treatment for neglected ruptures of the patellar tendon. Method: Patients who were included all had neglected patellar tendon ruptures that were initially misdiagnosed or had failed other treatment. Through a midline incision scar tissue was excised and two or three strong cerclage wires were used to approximate the patella and ruptured tendon. The wires were passed from the quadriceps tendon to the absorbable sutures in the tibia. No quadricepsplasty was necessary. Following the surgery immediate mobilisation was initiated without the use of a brace. The wires were removed six months following surgery. Results: Four patients were treated at an average of 29 months following the initial injury. The average follow- up was 26 months (range: 13 to 42 months). The average range of motion was 110 degrees. All patients had improved quadriceps strength, no extensor lag and had returned to work. Conclusion: We have described a simple effective method of treatment without the use of autograft or allograft. The strong cerclage wires allowed immediate mobilisation

Purpose of study. To study the effect of different shoes and orthotics have on patellar tendon tensile forces. Patellar tendinopathy is an overuse injury that affects tennis players and in high impact sports like basketball, volleyball and running has an incidence of 20%. The tensile forces in the patellar tendon can be reliably measured with an intratendinously placed fibre optic tube and wireless transmission device allows for dynamic testing. The biggest strain differentials have been confirmed in jumps from 30cm height. Tennis is played on 3 major different court surfaces and there is a variety of commercially designed tennis shoes on the market. Materials and methods. 6 male tennis players, ages 18–49 were enrolled for this study. A fibre optic cannula was placed in the middle of the proximal pole of patella tendon from lateral to medial direction in the dominant knee. The patellar tendon tensile forces deform the fibre optic cannula in turn modulating the light signal passing through the optic cannula. The drag in the fibre optic sensor signal was used to measure the tensile forces in the patellar tendon. MLTS 700 goniometer were utilized to measure and record the amount of flexion with each jump to standardize results for different shoes and orthotics. Results. The results of patellar tendon tensile forces measurements for different players, different shoes and orthotics showed no trend or statistical difference for any particular shoe or orthotic. Conclusions. Fibre optic measurements of the effect of different shoes on patellar tendon tensile forces did not show a distinct advantage for any shoe above another. 1 DISCLOSURE

In order to clarify the role of cytokines in the remodelling of the grafted tendon for ligament reconstruction we compared the responses to interleukin (IL)-1β, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-β1 of extrinsic fibroblasts infiltrating the frozen-thawed patellar tendon in rats with that of the normal tendon fibroblasts, in regard to the gene expression of matrix metalloproteinase (MMP)-13, using Northern blot analysis. We also examined, immunohistologically, the local expression of IL-1β, PDGF-BB, and TGF-β1 in fibroblasts infiltrating the frozen-thawed patellar tendon. Northern blot analysis showed that fibroblasts derived from the patellar tendon six weeks after the freeze-thaw procedure in situ showed less response to IL-1β than normal tendon fibroblasts with respect to MMP-13 mRNA gene expression. The immunohistological findings revealed that IL-1β was over-expressed in extrinsic fibroblasts which infiltrated the patellar tendon two and six weeks after the freeze-thaw procedure in situ, but neither PDGF-BB nor TGF-β1 was over-expressed in these extrinsic fibroblasts. Our findings indicated that IL-1β had a close relationship to matrix remodelling of the grafted tendon for ligament reconstruction, in addition to the commencement of inflammation during the tissue-healing process

We performed a biomechanical and histological study to clarify the effect of stress enhancement on the in situ frozen-thawed patellar tendon of the rabbit as a tendon autograft model. We used 48 Japanese White rabbits divided into three groups. In group 1, the patellar tendon underwent in situ freeze-thaw treatment with liquid nitrogen to kill intrinsic fibroblasts. In group 2, after similar treatment, the medial and lateral portions were resected so that the cross-sectional area was reduced by a third. In group 3, after treatment, the cross-sectional area was reduced by a half. In groups 2 and 3, the stress in the tendon was calculated theoretically to be 150% and 200% of the physiological stress during locomotion. Eight rabbits in each group were killed at three and six weeks, respectively. At three weeks, the mean values for the tensile strength of groups 2 and 3 were 113.7% and 75.7% of that of group 1, and at six weeks 101.2% and 57.4%, respectively. The tensile strength in group 3 was significantly lower than that in groups 1 and 2. The histological findings in group 2 were similar to those in group 1, although an acellular area appeared to be wider in the core portion compared with group 1 at each period. In group 3, the collagen bundles of the tendon were less organised than those of groups 1 and 2. Our findings showed that stress enhancement affects the remodelling of the frozen-thawed patellar tendon and that excessively high stress reduces the mechanical properties of the tendon. This indicates that high stress on the patellar tendon autograft should be avoided during ligament reconstruction

Obesity decreases patellar tendon stiffness in females but not males Introduction Patellar tendon (PT) injuries are frequent due to excessive mechanical loading during strenuous physical activity. PT injury incidence is higher in females and obese individuals. The reason behind higher tendon injury incidence in females and obese individuals might be structural changes in tendons such as stiffness or elasticity. Tendon stiffness can recently be quantified using shear wave elastography (SWE). We aimed to examine the stiffness of PT in healthy sedentary participants using this new technology. This prospective study was carried out with 58 (34 female, 24 male) healthy sedentary participants between the ages of 18–44 years (27.5±7.7 years). Body mass and body fat percentage were measured with the Bioelectrical Impedance method using Tanita BC-418 MA Segmental Body Composition Analyser (Tanita Corporation, Tokyo, Japan). Participants were subsequently categorized into ‘normal-weight’ (BMI < 23 kg/m2) and ‘obese’ (BMI>27.5 kg/m2). SWE of the PT was measured with the ACUSON S3000 (Siemens Medical Solution, Mountain Wiew, CA, USA) ultrasound device using the Siemens 9L4 (4–9 MHz) linear-array probe with the Virtual Touch Imaging Quantification® method. The measurement was performed by placing the US probe longitudinally on patellar tendon with knee flexed at 30°. The region between about 1 cm distal of patellar bone-tendon junction and 1 cm proximal of bone-tendon junction of tibia was used for PT stiffness measurement (Figure 1). Average of three successive measurements at 10 sec intervals was recorded as PT stiffness. PT stiffness was quantified with MATLAB Version 2015 (Mathworks, Massachusetts, USA) by converting colour data into numbers. PT stiffness, in males, in females, in normal males, in obese males, in normal females, and in obese females was 8.6±1.0 m/sec, 7.4±1.1 m/sec, 8.6±1.1 m/sec, 8.5±1.0 m/sec, 7.9±0.9 m/sec, and 6.2±0.9 m/sec, respectively. Average body fat percentage in males, in females, in normal males, in obese males, in normal females, and in obese females was 20.1±7.4 kg/m2, 30.1±8.1 kg/m2, 15.4±5.2 kg/m2, 24.7±4.6 kg/m2, 25.6±5.5 kg/m2, and 38.1±5.0 kg/m2, respectively. Males PT stiffness was higher when compared to that of females (p=0.000). PT stiffness was similar in obese and normal males (p=0.962) but obese females had lower PT stiffness compared to normal females (p=0.001). PT stiffness of females was lower than males and obesity decreased PT stiffness in females but not in males. The possible explanation of lower PT stiffness in females might be due to their higher estrogen levels that lead to a decrease in estradiol level and collagen synthesis. Lower tendon stiffness in obese females might be metabolic effects due to the increased adipose tissue that contains proteins such as adipokinome, chemerin, lipocalin 2, serum amyloid A3 and adiponectin. These proteins lead to disturbance of tendon homeostasis and decreased collagen content. Altered tendon homeostasis and decreased collagen content may lead to a decrease in tendon stiffness. Decreased PT stiffness in especially in obese women might be associated with increased risk of PT injury

Abstract. Objectives. The need for gender specific knee arthroplasty is debated. This research aimed to establish whether gender differences in patellar tendon moment arm (PTMA), a composite measure that characterises function of both the patellofemoral and tibiofemoral joints, are a consequence of knee size or other variation. Methods. PTMA about the instantaneous helical axis was calculated from positional data acquired using optical tracking. First, data post-processing was optimised, comparing four smoothing techniques (raw, Butterworth filtered, generalised cross-validation cubic spline interpolated and combined filtered/interpolated) using a fabricated knee. Then PTMA was measured during open-chain extension for N=24 (11 female) fresh-frozen cadaveric knees, with physiologically based loading and extension rates (420°/s) applied. Gender differences in PTMA were assessed before and after accounting for knee size with epicondylar width. Results. Combined smoothing enabled sub-mm accuracy (root-mean-squared (RMS) error 0.16mm, max error 0.47mm), whereas large errors were measured for raw (RMS 3.61mm, max 23.71mm), filtered-only (RMS 1.19mm, max 7.38mm) and interpolated-only (RMS 0.68mm, max 1.80mm) techniques. Before scaling, average PTMA throughout knee flexion was 46mm and mean, maximum, and minimum absolute values of PTMA were larger in males (mean differences >8mm, p<0.001), as were the PTMAs at terminal extension and flexion, and the change in PTMA from peak to terminal extension (differences >4mm, p<0.05). After scaling, the PTMA in deep flexion and the change in PTMA from peak to terminal extension were still larger in male knees (differences >2mm, p<0.05). The flexion angle of peak PTMA, unaffected by scaling, was closer to terminal extension for female knee (female 15°, male 29°, p<0.05). Conclusion. Gender differences in PTMA were identified both before and after accounting for knee size, with implications for gender-specific arthroplasty and musculoskeletal models. The developed measurement framework could also be applied in vivo for accurate measurement of the PTMA. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Two men, aged 21 and 50 years, were seen with ossification of the patellar tendon after injury to the knee in adolescence. They complained of pain and had patella alta. Large bony masses were excised from below the affected patellae. The patellar tendon was then reconstructed using a Leeds-Keio ligament. The results at six and ten years, respectively, were good, with neither patient having pain or an extension lag

Tendons and ligaments are similar in composition but differ in function. Simple anatomical definitions do not reflect the fact individual tendons and ligaments have unique properties due to their adaptation to a specific role. The patellar tendon is a structure of particular clinical interest. A null hypothesis was declared stating that the patellar tendon is not significantly different in terms of matrix composition and collagen fibril diameter to other tendons. The lateral and medial collateral ligaments (LCL, MCL), anterior and posterior cruciate ligaments (ACL, PCL), together with the long digital extensor, superfi-cial digital extensor and patellar tendons (LDET, SDFT, PT) were harvested from 3 cadaveric ovine hindlimbs. The extracellular matrix was assessed in terms of water, collagen and total sulphated glycosaminoglycan (GAG) content. The organisation of the collagen component was determined by an ultrastructural analysis of collagen fibril diameter distributions using electron microscopy, together with values for the collagen fibril index (CFI) and mass-average diameter (MAD). There were significant differences between ligaments and tendons. The PT had a bimodal collagen fibril diameter distribution with CFI72.9%, MAD 202nm, water content 53.1%, GAG content 2.3 g/mg and collagen content 73.7%, which was not significantly different from the other tendons. The results of this study support the null hypothesis suggesting that the patellar tendon is similar to other tendons and demonstrate that tendons have different characteristics to ligaments

We studied changes in patellar tendon length after reconstruction of the anterior cruciate ligament using either the medial third of the patellar tendon as a graft (n = 40) or a Leeds-Keio artificial ligament (n = 40). Both types of ligament replacement had been supplemented with a MacIntosh extra-articular lateral substitution. The mean change in length in the tendon graft group was 6% (SD 5.39); in the Leeds-Keio group it was 2.4% (SD 4.93). The change in length was significant in both groups, but shortening was more frequent and more severe in the tendon graft group. There was shortening of 10% or more in 25% of knees after patellar tendon graft and 7.5% after use of a Leeds-Keio prosthesis

We describe a new method for reconstructing the patellar tendon following combined injury to the patellar tendon and anterior cruciate ligament (ACL). Combined injuries to the patellar tendon and the ACL represent a rare and potentially serious injury pattern. The injury to the patellar tendon can often go undiagnosed at primary presentation. Reconstructive options for the patellar tendon are described but can be technically difficult, particularly if ipsilateral hamstring has been used for anterior cruciate ligament reconstruction. Evidence suggests combined injuries generally lead to poor long term outcome. We describe a case of a 26 year old male who presented with a reconstructed ACL and a patellar tendon deficient knee. Diagnosis was confirmed on Magnetic Resonance Imaging (MRI). Ipsilateral hamstrings had been used as donor for ACL reconstruction. An Achilles tendon allograft with distal bone block was used in combination with contralateral semitendinosus and gracilis autograft to reconstruct the three bundles of the patellar tendon. The patient experienced no postoperative complications and was followed up radiologically and clinically. Computer Topography imaging performed at 6 months post-operatively showed union of the bony Achilles tendon block. MRI performed 1 year post-operatively showed good incorporation of the tendinous grafts and no evidence of degeneration or tearing. Oxford knee score at 6 months post-operatively was 31/48. One year post-operatively full pre-injury activity level had been achieved. We believe this method to provide adequate strength and integrity, enabling early rehabilitation following this rare injury. It has also been shown to give a good functional outcome

Patella infera can cause knee pain and lead to patellofemoral osteoarthritis. Treatment is usually unsatisfactory. We describe a case of severe patella infera after operative treatment for fracture of the patella. We used Ilizarov external fixation and gradual lengthening of the patellar tendon. The patellar height was restored and the patient’s symptoms were much improved

Aims: To evaluate the morphologic changes in the patellar tendon 10 years after harvesting its central third for reconstruction of the anterior cruciate ligament, and examine the association between the morphologic changes and the occurrence of anterior knee pain of the patients. Methods: Thirty-one patients who had undergone an anterior cruciate ligament reconstruction using central-third bone-patellar tendon-bone autograft with a closure of the patellar tendon defect were included in this study. An ultrasonographic and Power Doppler examination was performed at a mean follow-up of 10 years. Results: Ultrasonography of the harvested patellar tendon showed intratendinous calcification in 9 patients, hypoechoic lesion in 20 patients, hyperechoic lesion in one patient, and peritendinous changes in one patient. No abnormality was visible in the contralateral (normal) patellar tendons of the 31 patients. The harvested patellar tendon was significantly thicker than the contralateral patellar tendon both at the proximal third (p=0.017) and at the distal third (p=0.020) of the tendon. Patellar osteophytes were more common in patients with anterior knee pain than without it (p=0.05). Conclusions: Sonographic morphologic changes of the patellar tendon were common 10 years after the harvesting procedure. Also, the harvested patellar tendon was significantly thicker than the normal patellar tendon

Introduction: Patello-femoral instability (PFI) and pain may be caused by anatomical abnormality. Many radiographic measurements have been used to describe the shape and position of the patella and femoral trochlea. Some are difficult to apply when dysplasia is present. This paper describes a simple new MRI measurement of the axial patellar tendon angle (APTA), and compares this angle in patients with and without patello-femoral instability. Method: Axial MRI images of the knee of 20 patients with PFI and 20 normal knees (isolated acute ACL rupture) were used for measurement. The angle between the patellar tendon and the posterior femoral condylar line was assessed at three levels from the proximal tendon to its insertion. Results: In normal knees, the APTA is 11 degrees of lateral tilt at all levels from the proximal tendon to its distal insertion. In PFI knees, the APTA is 32 degrees at the proximal tendon, 27 degrees at the joint line and 22 degrees at the distal insertion. The difference is significant (p< 0.001) at all levels. Discussion: Measurement of the APTA is reproducible and is easier than many other indices of patello-femoral anatomy. In PFI, the APTA is increased by 21 degrees at the proximal tendon and by 11 degrees at its distal insertion. In PFI, the patella is commonly tilted laterally. This is matched by the orientation of the patellar tendon. The increased tilt of the tendon is only partially corrected at its distal insertion with an abnormal angle of tibial attachment. When performing distal realignment procedures, angular correction as well as displacement may be appropriate

Objective: The aim of this study was to compare different patellar tendon repair constructs. Materials and Methods: Eight pairs of cadaveric legs were used to compare metal suture anchor repair with “standard” Krakow tendon suture through patella bone tunnels and steel box wire augmentation loop repair. Each leg was retested with box wire augmentation loop and simple 2/0 polyglactin suture repair. The repairs were tested by mounting the legs on a specially designed rig on a materials testing machine which allowed the leg to be cycled from 90° knee flexion to full extension. The specimens were cycled 1000 times at 0.25Hz or until the repair failed. Optical markers were attached to the leg which enabled the repair gap and knee angle to be monitored during testing (Smart Capture and Analyser Tracking system, Padua, Italy). Results: Six out of eight suture anchor repairs failed, all suture bone tunnel repairs with augmentation loops completed 1000 cycles. One out of 16 augmentation loop with simple 2/0 suture repair failed. For all specimens regardless of repair type that completed 1000 cycles there was no significant difference in repair gap distance. Conclusion: Suture anchors alone do not provide a strong enough construct for patellar tendon repair. The box wire augmentation loop is key to maintaining patellar tendon repair. Krakow tendon sutures secured through patellar bone tunnels do not provide additional benefit to a simple appositional suture and box wire augmentation loop

Patella infera may occur after reconstruction of the anterior cruciate ligament (ACL), high tibial osteotomy and total knee replacement (TKR). Restriction of movement of the knee and pain may result. Our aim was to compare the incidence and to assess the effects of patella infera after TKR and unicompartmental knee replacement (UKR). We reviewed radiographs of the knees of 84 patients who had had either TKR or UKR as part of a randomised, controlled trial. The length of the patellar tendon was measured on serial radiographs taken before, at eight months and at five years after operation. There was no significant change in the length of the patellar tendon after UKR, but a significant reduction was observed after TKR. Five years after the operation, the shortening of the tendon had increased to a mean of 3.5 mm. Of the knees with TKR reviewed at five years, 34% developed patella infera, defined as 10% or more of shortening, compared with 5% of those with UKR. Shortening was greatest in those knees which had required a lateral release; in this subgroup the mean shortening was 7.2 mm. Shortening correlated with restriction of movement and pain in the knee. Our study has shown that patella infera develops in most patients after TKR with lateral release, and in approximately 25% of patients after TKR without this additional procedure. Patella infera rarely occurs after UKR. It is associated with restriction of movement and pain in the knee. It may be an effect of the more extensive exposure required to perform TKR and may, in part, explain the better clinical results of UKR