Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model.

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p = 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendon-bone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel.     

The effect of muscle loading on flexor tendon‐to‐bone healing in a canine model

Previous tendon and ligament studies have demonstrated a role for mechanical loading in tissue homeostasis and healing. In uninjured musculoskeletal tissues, increased loading leads to an increase in mechanical properties, whereas decreased loading leads to a decrease in mechanical properties. The role of loading on healing tissues is less clear. We studied tendon‐to‐bone healing in a canine flexor tendon‐to‐bone injury and repair model. To examine the effect of muscle loading on tendon‐to‐bone healing, repaired tendons were either cut proximally (unloaded group) to remove all load from the distal phalanx repair site or left intact proximally (loaded group). All paws were casted postoperatively and subjected to daily passive motion rehabilitation. Specimens were tested to determine functional properties, biomechanical properties, repair‐site gapping, and bone mineral density. Loading across the repair site led to improved functional and biomechanical properties (e.g., stiffness for the loaded group was 8.2 ± 3.9 versus 5.1 ± 2.5 N/mm for the unloaded group). Loading did not affect bone mineral density or gapping. The formation of a gap between the healing tendon and bone correlated with failure properties. Using a clinically relevant model of flexor tendon injury and repair, we found that muscle loading was beneficial to healing. Complete removal of load by proximal transection resulted in tendon‐to‐bone repairs with less range of motion and lower biomechanical properties compared to repairs in which the muscle‐tendon‐bone unit was left intact. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

Extracorporeal shockwave enhanced regeneration of fibrocartilage in a delayed tendon‐bone insertion repair model

Fibrous tissue is often formed in delayed healing of tendon bone insertion (TBI) instead of fibrocartilage. Extracorporeal shockwave (ESW) provides mechanical cues and upregulates expression of fibrocartilage‐related makers and cytokines. We hypothesized that ESW would accelerate fibrocartilage regeneration at the healing interface in a delayed TBI healing model. Partial patellectomy with shielding at the TBI interface was performed on 32 female New Zealand White Rabbits for establishing this delayed TBI healing model. The rabbits were separated into the control and ESW group for evaluations at postoperative week 8 and 12. Shielding was removed at week 4 and a single ESW treatment was applied at week 6. Fibrocartilage regeneration was evaluated histomorphologically and immunohistochemically. Vickers hardness of the TBI matrix was measured by micro‐indentation. ESW group showed higher fibrocartilage area, thickness, and proteoglycan deposition than the control in week 8 and 12. ESW increased expression of SOX9 and collagen II significantly in week 8 and 12, respectively. ESW group showed a gradual transition of hardness from bone to fibrocartilage to tendon, and had a higher Vickers hardness than the control group at week 12. In conclusion, ESW enhanced fibrocartilage regeneration at the healing interface in a delayed TBI healing model. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:507–514, 2014.     

Rotator cuff healing using demineralized cancellous bone matrix sponge interposition compared to standard repair in a preclinical canine model

This Level II study assessed clinically relevant outcomes for repair of large, retracted infraspinatus tendons (ISTs) using a demineralized bone matrix (DBM) sponge (FlexiGraft) hydrated in platelet‐rich plasma (PRP) versus direct repair in a validated canine model. Adult research dogs (n = 10) were used. The IST was transected in each shoulder (n = 20) and randomized to direct repair or repair with DBM‐PRP interposition at 4 weeks posttransection. At 12 weeks postrepair, dogs were sacrificed, and the repair evaluated by magnetic resonance imaging (MRI), histology, and biomechanical testing. MRI and histology scores were significantly (p < 0.05) better in the DBM‐PRP shoulders. Biomechanical testing revealed significantly improved strength of the DBM‐PRP repairs at 5 and 10 mm of displacement, as well as for ultimate failure load. In this canine model of retracted IST repair, DBM‐PRP sponge hydrated in PRP was considered safe and effective. In addition, use of DBM‐PRP was associated with improved MRI and histologic appearance, and improved strength compared to direct repair. Clinical significance: Based on reported failure rates for repair of large, retracted rotator cuff tears, improving tendon‐to‐bone healing is critical. Use of DBM combined with PRP shows potential for addressing this critical clinical need. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:906–912, 2018.

     

The effect of rhPTH on the healing of tendon to bone in a rat model

Successful rotator cuff tendon repair depends on secure tendon‐to‐bone healing. Recombinant human parathyroid hormone (rhPTH) has been shown in multiple studies to accelerate bone healing. Recent studies have also shown that rhPTH is chondrogenic by increasing chondrocyte recruitment and differentiation. We hypothesized that rhPTH would improve tendon‐to‐bone healing in a rat rotator cuff repair model. One hundred and fourteen Sprague Dawley rats underwent division and repair of the supraspinatus tendon. Fifty seven rats received daily subcutaneous injections of 10 µg/kg of rhPTH. Rats were sacrificed at 3, 7, 14, 28, and 56 days for histologic and immunohistochemical analysis. In addition, rats in each group were sacrificed at 14, 28, and 56 days for biomechanical testing and micro CT analysis. At 2 weeks the controls had a significantly higher load to failure than the rhPTH group. At 28 and 56 days there were no differences in load to failure. rhPTH specimens had significantly higher stiffness at 56 days. MicroCT analysis showed that the rhPTH group had significantly greater total mineral content at all time points, as well as significantly higher bone volume (BV) at 14 and 28 days. Histologically, the rhPTH specimens had more fibrocartilage, osteoblasts, and blood vessels at all timepoints, with significantly better collagen fiber orientation at 28 and 56 days. Although treatment with rhPTH resulted in an increase in bone and mineralized fibrocartilage formation, as well as better collagen fiber organization, this did not translate into improved biomechanical properties. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:769–774, 2012     

Lubricin surface modification improves tendon gliding after tendon repair in a canine model in vitro

This study investigated the effects of lubricin on the gliding of repaired flexor digitorum profundus (FDP) tendons in vitro. Canine FDP tendons were completely lacerated, repaired with a modified Pennington technique, and treated with one of the following solutions: saline, carbodiimide derivatized gelatin/hyaluronic acid (cd‐HA‐gelatin), carbodiimide derivatized gelatin to which lubricin was added in a second step (cd‐gelatin + lubricin), or carbodiimide derivatized gelatin/HA + lubricin (cd‐HA‐gelatin + lubricin). After treatment, gliding resistance was measured up to 1,000 cycles of simulated flexion/extension motion. The increase in average and peak gliding resistance in cd‐HA‐gelatin, cd‐gelatin + lubricin, and cd‐HA‐gelatin + lubricin tendons was less than the control tendons after 1,000 cycles (p < 0.05). The increase in average gliding resistance of cd‐HA‐gelatin + lubricin treated tendons was also less than that of the cd‐HA‐gelatin treated tendons (p < 0.05). The surfaces of the repaired tendons and associated pulleys were assessed qualitatively with scanning electron microscopy and appeared smooth after 1,000 cycles of tendon motion for the cd‐HA‐gelatin, cd‐gelatin + lubricin, and cd‐HA‐gelatin + lubricin treated tendons, while that of the saline control appeared roughened. These results suggest that tendon surface modification can improve tendon gliding ability, with a trend suggesting that lubricin fixed on the repaired tendon may provide additional improvement over that provided by HA and gelatin alone. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:257–263, 2009     

Decreased muscle loading delays maturation of the tendon enthesis during postnatal development.

Physical environment influences the development and maintenance of musculoskeletal tissues. The current study uses an animal model to explore the role of the physical environment on the postnatal development of the supraspinatus tendon enthesis. A supraspinatus intramuscular injection of botulinum toxin A was used to paralyze the left shoulders of mice at birth. The supraspinatus muscles of right shoulders were injected with saline to serve as contralateral controls. The supraspinatus enthesis was examined after 14, 21, 28, and 56 days of postnatal development. Histologic assays were used to examine fibrocartilage morphology and percentage osteoclast surface. Micro-computed tomography was used to examine muscle geometry and bone architecture. At 14 days there were no differences between groups in fibrocartilage formation, muscle geometry, bone architecture, or osteoclast surface. When comparing groups at 21, 28, and 56 days, muscle volume was decreased, fibrocartilage development was delayed, mineralized bone was decreased, and osteoclast surface was higher at each timepoint in the botulinum group compared to the contralateral saline control group. Our results indicate that the development of the tendon enthesis is sensitive to its mechanical environment. A reduction in muscle loading delayed the development of the tendon-to-bone insertion site by impeding the accumulation of mineralized bone. Physical factors did not play a significant role in enthesis maturation in the first 14 days postnatally, implying that biologic factors may drive early postnatal development.     

The tensile strength of various peripheral circumferential repair techniques in canine flexor tendons

The purpose of this study was to evaluate the tensile strength of six peripheral circumferential suture techniques, using a variable number of suture strands. Transverse lacerations were made in 184 fresh frozen canine flexor profundus tendons and repaired using only a 6-0 Prolene circumferential suture. The six running suture techniques were: Simple, Simple-locking, Lembert, Halsted, Cross-stitch and Lin-locking, and 6, 10, 14, and 20 suture strands were used. For each technique, the tensile strength gradually increased with the increased number of suture strands. The tensile strength of the Lin-locking technique (19–34 N) was greater than that of the other techniques, followed by Cross-stitch (16–33 N), Halsted (10–25 N), Lembert (8–23 N), Simple (6–12 N), and Simple-locking (5–8 N). The Lin-locking had the best holding power, but it was technically the most complicated to place. The Cross-stitch had good tensile strength values. The Simple and the Simple-locking had the lowest tensile strengths. From the viewpoints of tensile strength and technical skill, the Cross-stitch may be preferable to other suture techniques.     

Achilles detachment in rat and stable gastric pentadecapeptide BPC 157: Promoted tendon-to-bone healing and opposed corticosteroid aggravation.

Stable gastric pentadecapeptide BPC 157 (BPC 157, as an antiulcer agent in clinical trials for inflammatory bowel disease; PLD-116, PL 14736, Pliva, no toxicity reported) alone (without carrier) ameliorates healing of tendon and bone, respectively, as well as other tissues. Thereby, we focus on Achilles tendon-to-bone healing: tendon to bone could not be healed spontaneously, but it was recovered by this peptide. After the rat's Achilles tendon was sharply transected from calcaneal bone, agents [BPC 157 (10 microg, 10 ng, 10 pg), 6alpha-methylprednisolone (1 mg), 0.9% NaCl (5 mL)] were given alone or in combination [/kg body weight (b.w.) intraperitoneally, once time daily, first 30-min after surgery, last 24 h before analysis]. Tested at days 1, 4, 7, 10, 14, and 21 after Achilles detachment, BPC 157 improves healing functionally [Achilles functional index (AFI) values substantially increased], biomechanically (load to failure, stiffness, and Young elasticity modulus significantly increased), macro/microscopically, immunohistochemistry (better organization of collagen fibers, and advanced vascular appearance, more collagen type I). 6alpha-Methylprednisolone consistently aggravates the healing, while BPC 157 substantially reduces 6alpha-methylprednisolone healing aggravation. Thus, direct tendon-to-bone healing using stabile nontoxic peptide BPC 157 without a carrier might successfully exchange the present reconstructive surgical methods.     

Tendon to bone tunnel healing—A study on the time‐dependent changes in biomechanics,bone remodeling,and histology in a rat model

Tendons and ligaments attach to bone through a transitional connective tissue with complex biomechanical properties. This unique tissue is not regenerated during healing, and surgical reattachment therefore often fails. The present study was designed to evaluate tendon healing in a bone tunnel and to evaluate the utilized rat model. Wistar rats (n = 61) were operated with the Achilles tendon through a bone tunnel in the distal tibia. Healing was evaluated at 2, 3, 4, and 12 weeks by biomechanical testing, bone mineral density and histology. After 2 weeks median (interquartile range) pull‐out force was 2.2 N (1.9). The pull‐out force increased chronologically, by 12 weeks fivefold to 11.2 N (11.4). Energy absorption, stiffness, and bone mineral density increased similarly. The histological analyses showed inflammation at early stages with increasing callus by time. Our data showed a slow healing response the first 4 weeks followed by an accelerated healing period, favoring that most of the gain in mechanical strength occurred later than 4 weeks postoperatively. These findings support the concern of a vulnerable tendon bone tunnel interface in the early stages of healing. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:216–223, 2015.     

Development of the supraspinatus tendon‐to‐bone insertion: Localized expression of extracellular matrix and growth factor genes

The adult healing response of the rotator cuff tendon‐to‐bone insertion site differs from the ordered process of insertion site development. Healing is characterized by disorganized scar and a lack of fibrocartilage formation, in contrast to the well organized fibrocartilaginous transition which forms during the normal development of the tendon‐to‐bone insertion. The purpose of this study was to localize the expression of a number of extracellular matrix and growth factor genes during insertion site development in order to guide future strategies for augmenting adult rotator cuff healing. The rotator cuff was morphologically distinct at 13.5 dpc (days postconception). Neo‐tendon was evident as a condensation of cells adjacent to bone. The interface between tendon and bone did not form into a mature fibrocartilaginous insertion until 21‐days postnatally, based upon the appearance of four distinct zones with a mineralized humeral head. Fibroblasts of the supraspinatus tendon expressed type I collagen at all timepoints. Type II collagen was first expressed by chondrocytes in the fibrocartilage and mineralized fibrocartilage at 7 days and persisted in the mineralized fibrocartilage at 56 days. Type X collagen was first expressed by the chondrocytes in the mineralized fibrocartilage at 14 days and persisted in the mineralized fibrocartilage at 56 days. A shift from TGF‐β3 to TGF‐β1 expression occurred at 15.5 dpc. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1621–1628, 2007     

Effects of trypsinization and mineralization on intrasynovial tendon allograft healing to bone

The purpose of the current study was to develop a novel technology to enhance tendon‐to‐bone interface healing by trypsinizing and mineralizing (TM) an intrasynovial tendon allograft in a rabbit bone tunnel model. Eight rabbit flexor digitorum profundus (FDP) tendons were used to optimize the trypsinization process. An additional 24 FDP tendons were stratified into control and TM groups; in each group, 4 tendons were used for in vitro evaluation of TM and 8 were transplanted into proximal tibial bone tunnels in rabbits. The samples were evaluated histologically and with mechanical testing at postoperative week 8. Maximum failure strength and linear stiffness were not significantly different between the control and TM tendons. A thin fibrous band of scar tissue formed at the graft‐to‐bone interface in the control group. However, only the TM group showed obvious new bone formation inside the tendon graft and a visible fibrocartilage layer at the bone tunnel entrance. This study is the first to explore effects of TM on the intrasynovial allograft healing to a bone tunnel. TM showed beneficial effects on chondrogenesis, osteogenesis, and integration of the intrasynovial tendon graft, but mechanical strength was the same as the control tendons in this short‐term in vivo study. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:468–474, 2015.     

Characteristics of the rat supraspinatus tendon during tendon-to-bone healing after acute injury.

Rotator cuff repair is known to have a high failure rate. Little is known about the natural healing process of the rotator cuff repair site, hence little can be done to improve the tendon's ability to heal. The purpose of this study was to investigate the collagen formation at the early repair site and to localize TGFbeta-1 and 3 during early healing and compare their levels to cell proliferation and histological changes. Bilateral supraspinatus tendons were transected and repaired in 60 rats. Specimens were harvested and evaluated at 0, 1, 3, 7, 10, 28, and 56 days. Histological sections were evaluated for cell morphology. Immunohistochemistry and in situ hybridization was performed to localize protein and mRNA for collagen types I and III and TGFbeta-1 and 3. Proliferating cell nuclear antigen (PCNA) assay was performed to measure cell proliferation, and cells were counted to determine cell density. Biomechanical properties were evaluated. Repair tissue demonstrated an initial inflammatory response with multinucleated cells present at 1 and 3 days, and lymphocytes and plasma cells presents at 7 and 10 days. Capillary proliferation began at 3 days and peaked at 10 days. Ultimate force increased significantly over the time period studied. Collagen I protein and mRNA significantly increased at 10 days, and reached a plateau by 28 and 56 days. Collagen III showed a similar trend, with an early increase, and remained high until 56 days. TGFbeta-1 was localized to the forming scar tissue and showed a distinct peak at 10 days. TGFbeta-3 was not seen at the healing insertion site. Cell proliferation and density followed the same trend as TGFbeta-1. A wound healing response does occur at the healing rotator cuff insertion site, however, the characteristics of the tendon after healing differ significantly from the uninjured tendon insertion site at the longest time-point studied. A distinctive collagen remodeling process occurred with an initial increase in the formation of collagen types I and III followed by a decrease toward baseline levels seen at time 0. Growth factor TGFbeta-1 was localized to repair tissue and coincided with a peak in cell proliferation and cellularity. Repair sites remained unorganized histologically and biomechanically inferior in comparison to previously described uninjured insertion sites.     

Tendon gradient mineralization for tendon to bone interface integration

Tendon‐to‐bone integration is a great challenge for tendon or ligament reconstruction regardless of use of autograft or allograft tendons. We mineralized the tendon, thus transforming the tendon‐to‐bone into a “bone‐to‐bone” interface for healing. Sixty dog flexor digitorum profundus (FDP) tendons were divided randomly into five groups: (1) normal FDP tendon, (2) CaP (non‐extraction and mineralization without fetuin), (3) CaPEXT (Extraction by Na₂HPO₄ and mineralization without fetuin), (4) CaPFetuin (non‐extraction and mineralization with fetuin), and (5) CaPEXTFetuin (extraction and mineralization with fetuin). The calcium and phosphate content significantly increased in tendons treated with combination of extraction and fetuin compared to the other treatments. Histology also revealed a dense mineral deposition throughout the tendon outer layers and penetrated into the tendon to a depth of 200 µm in a graded manner. Compressive moduli were significantly lower in the four mineralized groups compared with normal control group. No significant differences in maximum failure strength or stiffness were found in the suture pull‐out test among all groups. Mineralization of tendon alters the interface from tendon to bone into mineralized tendon to bone, which may facilitate tendon‐to‐bone junction healing following tendon or ligament reconstruction. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1713–1719, 2013     

Generation of tendon-to-bone interface "enthesis" with use of recombinant BMP-2 in a rabbit model.

The anatomical structure at bone-tendon and bone-ligament interfaces is called the enthesis. Histologically, the enthesis is characterized by a transitional series of tissue layers from the end of the tendon to bone, including tendon, fibrocartilage, calcified fibrocartilage, and bone. This arrangement yields stronger direct connection of the soft tissues to bone. In surgical repair, the enthesis has proven difficult to reproduce, and the success of ligament-bone bonding has depended on the fibrous attachment that forms after any ligament reconstructions. In this study, we attempted to generate a direct-insertion enthesis in two stages. First, recombinant human bone morphogenetic protein-2 (rhBMP-2) was injected into the flexor digitorum communis tendon in the rabbit hind limb to induce ectopic ossicle formation. In a second step, the resultant tendon/ossicle complex was then surgically transferred onto the surface of the rabbit tibia to generate a stable tendon-bone junction. One month following surgery, histomorphological examination confirmed direct insertion of tendon-bone structures in the proximal tibia of the rabbit. Ultimate failure loads of the BMP-2-generated tendon-bone junction were significantly higher than in the control group (p < 0.01). These findings suggest that it is possible to successfully regenerate a direct tendon-to-bone enthesis. Use of this approach may enable successful reconstruction of joints rendered unstable after ligamentous rupture or laxity after anterior cruciate ligament injury.     

PDGF-BB released in tendon repair using a novel delivery system promotes cell proliferation and collagen remodeling.

The purpose of this study was to promote fibroblast proliferation and collagen remodeling in flexor tendon repair through sustained delivery of platelet derived growth factor (PDGF-BB). The release kinetics of PDGF-BB from a novel fibrin matrix delivery system was initially evaluated in vitro. After the in vivo degradation rate of the fibrin matrix was determined using fluorescently tagged fibrin, PDGF-BB was delivered to the site of flexor tendon repair in vivo in a canine model. The effect of PDGF-BB on intrasynovial tendon healing was studied using histology-based assays (cell density, proliferation, and type I collagen expression) and by measuring total DNA levels and reducible collagen crosslink levels. The fibrin matrix delivery system provided sustained release of PDGF-BB in vitro at a rate modulated by the ratio of heparin to growth factor. In vivo, the fibrin matrix remained at the repair site for more than 10 days. Delivery of PDGF-BB led to a qualitative increase in cell density, cell proliferation, and type I collagen mRNA expression. PDGF-BB also led to statistically significant increases in total DNA (20% increase at 7 days, 18% increase at 14 days) and reducible collagen crosslinks (30% increase at 7 days). Sustained delivery of growth factors may be achieved using a novel fibrin-based delivery system. PDGF-BB delivery increased cell proliferation and matrix remodeling and thus may accelerate flexor tendon healing.     

Local administration of alendronate reduced peri‐tunnel bone loss and promoted graft‐bone tunnel healing with minimal systemic effect on bone in contralateral knee

Continued systemic administration of alendronate was reported to reduce peri‐tunnel bone resorption and promoted graft‐bone tunnel healing at the early stage post‐anterior cruciate ligament (ACL) reconstruction. However, systemic increase in bone mineral density (BMD) in the contralateral intact knee was observed. We tested if single local administration of alendronate into the bone tunnel during ACL reconstruction could achieve similar benefits yet without the systemic effect on bone. Seventy‐two rats with unilateral ACL reconstruction were divided into three groups: saline, low‐dose (6 μg/kg) and mid‐dose (60 μg/kg) alendronate. For local administration, alendronate was applied to the bone tunnels for 2 min before graft insertion and repair. At weeks 2 and 6, the reconstructed complex was harvested for high‐resolution computed tomography (vivaCT) imaging followed by biomechanical test or histology. Our results showed that local administration of low‐dose alendronate showed comparable benefits on the reduction of peri‐tunnel bone loss, enhancement of bone tunnel mineralization, tunnel graft integrity, graft osteointegration and mechanical strength of the reconstructed complex at early stage post‐reconstruction, yet with minimal systemic effect on mineralized tissue at the contralateral intact knee. A single local administration of alendronate at the low‐dose therefore might be used to promote early tunnel graft healing post‐reconstruction. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1897–1906, 2013     

Alendronate prevents femoral periprosthetic bone loss following total hip arthroplasty: prospective randomized double-blind study.

Following total hip arthroplasty (THA), femoral periprosthetic bone undergoes a remodeling process that results in bone loss in its proximal regions that may compromise the long-term outcome of THA. Periprosthetic bone loss mainly occurs during the first postoperative months. The question is whether a postoperative treatment with alendronate is effective in reducing periprosthetic bone loss and which doses and duration of treatment are required. In a 12-month prospective, randomized double-blind study, 51 patients undergoing cementless THA were treated postoperatively either with a daily dose of 20 mg alendronate for 2 months and 10 mg for 2 months thereafter (group I), with 20 mg of alendronate for 2 months and 10 mg for 4 months thereafter (group II), or treated with placebo (group III). Proximal femoral bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry (DEXA) and serum biochemical markers of bone turnover bone specific alkaline phosphatase, osteocalcin, and C-terminal telopeptides (CTX-I) were assayed. Six months of alendronate treatment significantly reduced (p<0.001) bone loss in proximal medial region (-10%) compared with placebo (-26%). All biochemical markers of bone turnover were suppressed by alendronate. These data suggest that alendronate administered for the first 6 postoperative months following THA was effective in preventing early periprosthetic bone loss.     

Remodeling of the gliding surface after flexor tendon repair in a canine model in vivo.

Maintaining a smooth lubricated surface between the flexor tendon and sheath after tendon repair is very important for restoration of digit function. We studied the tendon surface after tendon repair mechanically in a canine model in vivo by measuring frictional force. One hundred and twenty flexor digitorum profundus (FDP) tendons were lacerated to 80% of their cross-section and repaired with either a modified Kessler (MK) or Becker (MGH) repair. The postoperative therapeutic regimen was either synergistic wrist and digit motion (SWM) or passive digit flexion and extension with the wrist fixed in 45 degrees of flexion (FIX). The dogs were sacrificed at one, three, or six weeks postoperatively. Thirty six FDP tendons from normal paws served as the control group, with each control tendon tested in two different conditions: intact and immediately after partial laceration and repair (0 time), making a total of five different timing points (intact, 0 time, one week, three weeks, and six weeks) for each repair type and each postoperative therapy. Frictional force between tendon and proximal pulley was evaluated after breaking any adhesions. Compared to intact tendons, friction was significantly increased immediately after tendon repair. The friction of the MK repair was significantly less than that of the MGH repair at all time and therapy groups, except at six weeks in the SWM group. For the MGH repair, at six weeks friction in the SWM group was significantly less than friction in the FIX group. This study showed that postoperative tendon gliding depends on the method of tendon repair and the postoperative therapy regimen. Furthermore, we have demonstrated that the gliding surface after tendon repair remodels with time.