Predicting ACL Reinjury from Return to Activity Assessments at 6-months Post-Surgery: A Prospective Cohort Study

CONTEXT

Return to activity(RTA) assessments are commonly administered following ACL-Reconstruction(ACLR) to manage post-operative progressions back to activity. To date, there is little knowledge on the clinical utility of these assessments to predict patient outcomes such as secondary ACL injury once returned to activity.

OBJECTIVE

To identify what measures of patient function at 6-months post-ACLR best predict return to activity and second ACL injury at a minimum of 2-years following ACLR.

DESIGN

Prospective-cohort Setting: Laboratory Patients: A total of 234 patients with primary, unilateral ACLR completed functional assessments at approximately 6-months post-ACLR. A total of 192(82%) completed follow-up ≥ 2-years post ACLR.

MAIN OUTCOME MEASURES

Six-month functional assessments consisted of patient reported outcomes, isokinetic knee flexor and extensor strength, and single-leg hopping. The ability to return to activity and secondary ACL injury were collected at a minimum of two-years following ACLR.

RESULTS

In patients who did RTA(n=155), a total of 44(28%) individuals had a subsequent ACL injury; graft n=24(15.5%), contralateral ACL n=20(13%). A greater proportion of females had a secondary injury to the contralateral ACL(15/24, 63%) whereas a greater proportion of males reinjured the ipsilateral ACL graft(15/20, 75%, P=.017) Greater knee extension symmetry at 6-months increased the probability of reinjury(B=.016, P=.048). In patients who RTA before 8-months, every 1% increase in quadriceps strength symmetry at 6-months increased the risk of reinjury by 2.1%(B=.021, P=.05). In patients who RTA after 8-months, every month that RTA was delayed reduced the risk of reinjury by 28.4%(B=-284, P=.042).

CONCLUSIONS

Patients with more symmetric quadriceps strength at 6-months post ACLR were more likely to experience another ACL rupture, especially in those who returned to sport earlier than 8-months after the index surgery. Clinicians should be cognizant that returning high functioning patients to activity earlier than 8-months post-ACLR may place them at an increased risk for reinjury.

Nonlinear Viscoelastic Behavior of Human Knee Ligaments Subjected to Complex Loading Histories

The nonlinear viscoelastic structural response of the major human knee ligaments when subjected to complex loading histories is investigated, with emphasis on the collateral ligaments. Bone-ligament-bone specimens are tested in knee distraction loading, where the ligaments are in the anatomical position corresponding to a fully extended knee. Temporal nonlinearities for time scales in the range of 1<or=t <or=500 s are characterized with a dedicated series of loading histories. In particular, the response to several complex sequences of step-and-hold tests and loading-unloading cycles is investigated. The separability of the time and deformation dependent behavior, as assumed for the often used quasi linear viscoelastic (QLV) theory, is found to be insufficient for describing the response in the time range considered. Non-recoverable inelastic flow is observed in this time range. A phenomenological 1-dimensional nonlinear viscoelastic model that qualitatively describes the experimentally observed inelastic phenomena is presented.

Pedestrian injuries: viscoelastic properties of human knee ligaments at high loading rates

OBJECTIVE

Accidents involving pedestrians are very common, and often lead to severe injuries to the lower extremities. In a large portion of pedestrian-automobile collisions, knee ligament injuries are sustained. In this study, the viscoelastic properties of the four major human knee ligaments were investigated at loading rates representative for pedestrian-automobile collisions.

METHODS

Bone-ligament-bone specimens were tested in knee distraction loading. The collateral ligaments and the separate functional bundles of the cruciate ligaments were tested in the anatomical position corresponding to a fully extended knee. A series of step-and-hold tests and ramp tests at different rates were conducted to characterize the time-dependent behavior of the knee ligaments for deformation rates associated with the pedestrian impact loading environment. The quasi linear viscoelastic (QLV) theory was used to describe the structural response of the knee ligaments and averaged parameters for this model were determined.

RESULTS

The QLV theory was found to be applicable for the time range that is relevant for pedestrian-automobile collisions. The structural behavior of the knee ligaments was found to be particularly rate-sensitive for high elongation rates, as occur during these collisions. The ligament stiffness was found to increase with age for both the collateral ligaments and with weight for the medial collateral ligament.

CONCLUSIONS

For the loading conditions that are relevant for pedestrian-automobile collisions, the use of the QLV model for the description of the mechanical behavior of knee ligaments is appropriate. The rate-sensitivity is particularly important for these extreme loading conditions. The relaxation behavior was found to be consistent between different ligament types and samples. Variations due to donor anthropometry were found predominantly for the instantaneous elastic behavior.

Treatment with insulin-like growth factor-1 increases chondrogenesis by periosteum in vitro

The repair of defects in articular cartilage with hyaline tissue that is resilient to wear is a challenging problem. Fibrocartilaginous tissue forms in response to injury through the articular surface and degenerates under mechanical load. Because periosteum contains cells, which are capable of synthesizing cartilage matrix proteins, it has been used to repair defects in articular surfaces. Treatment of periosteal grafts with growth factors, particularly those that elicit chondrocyte gene expression, may improve tissue regeneration. Gene expression by periosteal explants in vitro was measured. Expression of type II collagen and aggrecan mRNA was increased in response to treatment with IGF-I. Furthermore, IGF-I treatment caused an increase in type II collagen and aggrecan mRNA that was time and concentration dependent. The effect of short and long-term (continuous) incubations was compared to determine if a pretreatment could be used to condition a graft for subsequent surgical use. Short-term incubation in vitro with IGF-I followed by incubation without IGF-I was nearly as effective at increasing expression of type II collagen and aggrecan mRNA as incubation for the same length of time with IGF-I present continuously in the culture media. Treatment with IGF-I also produced cell clustering and nodule formation which are indicative of chondrogenesis. These results suggest that pretreatment with IGF-I in vitro may enhance the effectiveness of a graft to produce hyaline cartilage in vivo. Whether the cellular and molecular changes we have observed can lead to the formation of tissue that withstands the mechanical forces exerted by weight bearing remains to be determined.

Component size asymmetry in bilateral total knee arthroplasty

A review of 268 consecutive patients undergoing bilateral total knee arthroplasty (TKA) was performed to determine whether component size asymmetry exists in patients undergoing bilateral TKAs. Component sizes were selected based on preoperative radiographic templating and intraoperative sizing measurements irrespective of the component sizes chosen for the other knee. All radiographs were evaluated according to described criteria. Component sizes used for the femur, tibia, and patella were compared between the right and left knees. Of the 268 bilateral TKAs, 18 (6.7%) femoral components varied in size between right and left knees. There were no statistical differences for patellar or tibial component size asymmetry or knee function pre- or postoperatively. Patients with asymmetrically sized femoral components had no statistical difference between left and right knees with respect to knee score, pain, function, range of motion, incidence of lateral release, or complications.

Progressive articular cartilage loss following radiofrequency treatment of a partial-thickness lesion

Arthroscopic debridement of partial-thickness articular cartilage lesions is a common orthopaedic procedure. Radiofrequency treatment has rapidly gained clinical acceptance despite the lack of prospective studies involving second-look arthroscopy to determine long-term sequelae. We report a case in which a partial-thickness lesion that had been treated with radiofrequency ablation showed progressive thinning of the articular surface.

Modern concepts in arthroscopic Bankart repair

The purpose of this report is to review recent advances in Bankart repair that allow it to be performed arthroscopically. Metallic implants in the form of staples, screws, or rivets were used initially, but problems with loosening of implants has prompted development of alternative devices and techniques. A modified form of the transglenoid suturing technique used in open Bankart repair has been used successfully but is associated with an increased risk of soft tissue complications. The use of absorbable tacks avoids some of the complications associated with this approach, but the ability to advance the capsule to reduce the volume is limited. Recently, the use of suture anchors has been described for arthroscopic Bankart lesion repair. However, the ability of these anchoring systems to advance and reduce the capsular volume is limited, and the arthroscopic techniques are technically demanding. One particularly innovative suture anchor system uses a bioabsorbable suture anchor with an integrated suture passing system. This self-contained implant allows multiple passes with suture through the capsule, followed by attachment to the glenoid with the bioabsorbable anchor. This procedure allows the capsule to be advanced by passing suture through before it is anchored to the glenoid, thereby reducing capsular volume to help restore shoulder stability.

Innovative techniques in arthroscopic meniscal repair

Advanced techniques for arthroscopic repair of meniscal tears offer new ways to repair the meniscus and reduce the rate of long-term arthrosis. The new all-inside technique reduces complications, morbidity, and surgical time as compared to the inside-out or outside-in methods of repair. Application of biomaterial technology to new implants used for all-inside arthroscopy show early promising clinical results. The purpose of this report is to describe new biomaterials and techniques being used successfully in arthroscopic surgery on the meniscus.

Acute noncontact compartment syndrome

Although acute compartment syndrome is considered a surgical emergency, controversies exist regarding diagnosis, surgical indications, and techniques of management. Acute compartment syndrome is associated with numerous causes, including fractures, crush injuries, burns, soft tissue injuries, and vascular trauma. Prolonged positioning of an extremity has not been previously described as a cause of compartment syndrome. The authors present a case of an acute compartment syndrome occurring because of prolonged extrication after a motor vehicle accident and without direct trauma to the involved extremity.

Marrow stromal cells embedded in alginate for repair of osteochondral defects

Articular cartilage defects of sufficient size ultimately degenerate with time, leading to arthritic changes. Numerous strategies have been used to address full-thickness cartilage defects, yet none thus far has been successful in restoring the articular surface to its preinjury state. We compared the effects of agarose, alginate, and type I collagen gels on the expression of cartilage-specific markers from rabbit marrow stromal cells and then assessed the in vivo effects of cells seeded in alginate beads on the repair of full-thickness osteochondral defects in the rabbit model. Marrow aspirates from rabbits were cultured and the stromal population selected. Marrow stromal cells were then placed in either 1.2% w/v alginate, type I collagen gels (3 mg/mL), or 0.5% agarose suspension culture. After 2, 5, 10, and 20 days in culture, the RNA was extracted and analyzed by reverse transcription polymerase chain reaction for the cartilage-specific markers aggrecan and type II collagen. The strongest increase in aggrecan and type II collagen gene expression was found in the agarose suspension followed by alginate; type I collagen gels induced the lowest levels. Alginate beads were chondrogenic and maintained their size and consistency over time in culture, whereas the cell-seeded collagen gels invariably contracted. Full-thickness defects measuring 3 x 6 mm x 3 mm deep were then created in the medial femoral condyles of rabbit knees and filled with alginate beads, alginate beads seeded with stromal cells, or left empty. Alginate beads containing stromal cells remained within the defects and progressively filled the defects with regenerate tissue. Histologic analysis showed viable, phenotypically chondrogenic cells in the defects. The matrix stained positive with safranin O, indicating proteoglycan synthesis, and bonding between the regenerate and host tissue was excellent. We have shown quantitative differences in the chondrogenic effects of the biomaterials tested. Alginate induces the chondrogenic phenotype in marrow stromal cells in vitro, and possesses the necessary physical characteristics and handling properties to support cells and serve as a carrier to fill full-thickness osteochondral defects in vivo.

Lower extremity compensations following anterior cruciate ligament reconstruction

BACKGROUND AND PURPOSES

Several studies have demonstrated that patients with knee injury scored within a normal range during one-legged hop tests, yet showed quadriceps femoris muscle weakness with non-weight-bearing isokinetic testing. This study evaluated lower-extremity kinetics while subjects performed a single-leg vertical jump (VJ) and a lateral step-up (LSU) in an attempt to explain this phenomenon.

SUBJECTS AND METHODS

Using a motion analysis and force platform system, hip, knee, and ankle extension moments of 20 subjects with anterior cruciate ligament (ACL) reconstructions and 20 matched subjects were measured while they performed an LSU and a VJ.

RESULTS

An analysis of variance revealed that the knee extension moment of the ACL-reconstructed extremity was lower than that of the uninjured and matched extremities during the LSU, VJ take-off, and VJ landing. However, there was no difference in summated extension moment (hip + knee + ankle) among extremities during the LSU and VJ take-off. The summated extension moment of the ACL-reconstructed extremity during VJ landing was less than that of the uninvolved and matched extremities.

CONCLUSION AND DISCUSSION

These results suggest that the hip or ankle extensors may compensate for the knee extension moment deficit. The decrease in summated extension moment in the ACL-reconstructed extremity during VJ landing represents inadequate attenuation of landing forces, which may expose the skeleton and joint structures to injury.

Analysis of routine histological evaluation of tissues removed during primary hip and knee arthroplasty

BACKGROUND

It has often been hospital policy to send all resected specimens obtained during a total hip or knee arthroplasty for histological evaluation. This practice is expensive and may be unnecessary. We sought to determine the ability of surgeons to diagnose primary joint conditions correctly, and we attempted to identify any possible risks to the patient resulting from the omission of routine histological evaluation of specimens at the surgeon's discretion. Our objective was to ascertain whether routine histological evaluation could be safely omitted from the protocol for primary hip and knee arthroplasty without compromising the care of the patient.

METHODS

A total of 1388 consecutive arthroplasties in 1136 patients were identified from a database of primary total hip and knee arthroplasties that was prospectively maintained by the senior one of us. Follow-up data obtained at a mean of 5.5 years (range, two to ten years) were available after 92 percent (1273) of the 1388 arthroplasties. The preoperative diagnosis was determined from the history, findings on clinical examination, and radiographs. The intraoperative diagnosis was determined by gross inspection of joint fluid, articular cartilage, synovial tissue, and the cut surfaces of resected specimens. The combination of the preoperative and intraoperative diagnoses was considered to be the surgeon's clinical diagnosis. All resected specimens were sent for routine histological evaluation, and a pathological diagnosis was made. Attention was given to whether a discrepancy between the surgeon's clinical diagnosis and the pathological diagnosis altered the management of the patient. The original diagnoses were updated with use of annual radiographs and clinical assessments. The cost of histological examination of specimens obtained at arthroplasty was determined by consultation with hospital administration, accounting, and pathology department personnel.

RESULTS

A pathological fracture or an impending fracture was diagnosed preoperatively and confirmed intraoperatively during twelve of the 1388 arthroplasties. Histological analysis demonstrated malignancy in specimens obtained during eleven of these arthroplasties and evidence of a benign rheumatoid geode in the specimen obtained during the twelfth arthroplasty. The preoperative and intraoperative diagnoses made before and during the remaining 1376 arthroplasties were benign conditions, which were confirmed histologically in all patients. No diagnosis changed during the follow-up period. As demonstrated by a comparison with the histological diagnosis, the surgeon's clinical diagnosis of malignancy had a sensitivity of 100 percent (95 percent confidence interval, 74.0 to 100 percent), a specificity of 99.9 percent (95 percent confidence interval, 99.6 to 100 percent), a positive predictive value of 91.7 percent (95 percent confidence interval, 64.6 to 98.5 percent), and a negative predictive value of 100 percent (95 percent confidence interval, 99.7 to 100 percent). There was a discrepancy between the preoperative and intraoperative diagnoses associated with eleven arthroplasties. All eleven intraoperative diagnoses were correct, as confirmed histologically. Excluding the patients who had a pathological or impending fracture, the accuracy of the surgeon's preoperative diagnosis was 99.2 percent (95 percent confidence interval, 98.6 to 99.5 percent). When the intraoperative and preoperative diagnoses were combined, the accuracy was 100 percent (95 percent confidence interval, 99.7 to 100 percent). Histological evaluation at our hospital resulted in total charges, including hospital costs and professional fees, of $196.27 and a mean total reimbursement of $102.59 per evaluation. In our series of 1136 patients with 1388 arthroplasties, these costs could have been eliminated for all but the twelve patients who had a suspected malignant lesion and the one patient in whom pigmented villonodular synovitis was found. (ABSTRACT

Bone contusions of the posterior lip of the medial tibial plateau (contrecoup injury) and associated internal derangements of the knee at MR imaging

PURPOSE

To determine if there are any predictable patterns of internal derangement associated with a bone contusion of the posterior lip of the medial tibial plateau at magnetic resonance (MR) imaging and to offer a biomechanical explanation for the findings.

MATERIALS AND METHODS

A retrospective review of 215 consecutive MR examinations for knee trauma was conducted to identify contusions of the posterior lip of the medial tibial plateau. Any additional contusions and internal derangements were documented in the cases with these contusions. Medical charts and arthroscopic results, when available, were reviewed for mechanisms of injury.

RESULTS

The specific medial tibial contusion was demonstrated in 25 of 215 (12%) knee MR examinations. Associated anterior cruciate ligament (ACL) tears were found in 25 of the 25 (100%) examinations. Injury to the meniscocapsular junction (14 of 25) or a peripheral tear of the posterior horn of the medial meniscus (10 of 25) occurred in a combined 96% of the cases. Lateral compartment contusions were noted in 24 (96%) cases. Pivot, twisting, or valgus forces were reported mechanisms of injury.

CONCLUSION

Contusions involving the posterior lip of the medial tibial plateau may result from a contrecoup impaction injury directly following an ACL tear, as the knee reduces. These contusions are almost always associated with a far peripheral meniscal tear or with a meniscocapsular junction injury affecting the posterior horn of the medial meniscus.

Transient posterior knee pain with the meniscal arrow

A 31% incidence of focal posterior knee pain was noted in our initial experience with all-inside meniscal repair using the absorbable Meniscal Arrow system (Bioscience, Tampere, Finland). The pain was transient, resolved by 6 months in all cases, and was unrelated to the length of implant. A typical case is presented to assist surgeons in counseling patients who experience transient posterior knee pain after meniscal repair with this system.

Postoperative radiographs after total knee arthroplasty: a cost-containment strategy

We reviewed a single surgeon's experience with 646 consecutive total knee arthroplasties (TKAs) performed over a 6-year period to determine whether routine in-hospital radiographs could be safely avoided. Five hundred fourteen patients underwent 589 primary and 57 revision TKAs. One hundred thirty-two patients had bilateral procedures. Radiographs were obtained during the index hospitalization for 12 (2%) knees and were ordered selectively to assess femoral notching > or =3 mm, concomitant osteotomy, bulk allograft reconstruction, stem extension relative to existing hardware or screw holes, or falls during the index hospitalization. Radiographs were delayed until the initial postoperative office visit for the remaining 634 (98%) knees. Six hundred seventeen of 646 knees (96%) were evaluated at a mean follow-up of 4.3 years (range: 2 to 8 years). No patient experienced any complication that was considered to be attributable to not obtaining earlier postoperative radiographs. Three patients experienced late fractures and 7 patients developed perioperative soft-tissue complications or infections. None of these cases were adversely affected by delaying the initial postoperative radiographs. Eliminating in-hospital radiographs with radiologist interpretation resulted in a potential savings of $246 in hospital charges, $198 in private insurance reimbursements, and $65 in hospital costs per TKA. These findings indicate that radiographs following TKA can be delayed in most cases until the first postoperative office visit without compromising patient care.

The effect of pretwisting the ACL autograft on knee laxity

This study was undertaken to determine whether pretwisting the bone-patellar tendon-bone autograft during primary anterior cruciate ligament (ACL) reconstruction had any effect on knee laxity. Patients were assigned to have twisted or nontwisted autografts based on the date of ACL reconstruction. The control group was comprised of 60 patients without graft twist, and the twist group was comprised of 60 patients who had 90 degrees of external twist applied to the graft prior to tibial fixation to reproduce the anatomic external twist of the native ACL. The average patient age was 28.8 years for the control group and 28.3 years for the twist group. Males accounted for 68% of the control patients and 73% of the twist patients. Meniscal tears were present in 45% of control and 52% of twist patients. Reconstructions were performed using an endoscopic, single-incision technique with interference screw fixation in the femur. Follow-up examination with KT-2000 arthrometry was performed when patients were within 10% of strength of the uninjured leg by isokinetic testing. KT-2000 testing at 30 lb revealed a mean side-to-side difference for reconstructed versus noninvolved knees of 1.06 for control patients and 1.08 for twist patients. The difference between the two groups was not statistically significant. All but three control and two twist patients had a Lachman and an anterior drawer examination graded as 0 to 1+. This difference also was not statistically significant. There were no clinical failures in either group. Furthermore, there was no statistically significant difference between groups clinically or by arthrometry when comparing tibial fixation with an interference fit screw versus suture fixation to a unicortical post. These results indicate that pretwisting the patellar tendon autograft in ACL reconstruction has no significant short-term effect on knee laxity as determined by instrumented testing or clinical examination.

Acutely injured knee: effect of MR imaging on diagnostic and therapeutic decisions

PURPOSE

To assess the effect of knee magnetic resonance (MR) imaging on the diagnosis and management of acute knee injury.

MATERIALS AND METHODS

Two orthopedic knee surgeons prospectively completed pre- and post-MR imaging questionnaires on 84 of 91 consecutive patients with acute knee injury. The pre- and post-MR imaging clinical diagnoses, certainty regarding these diagnoses, other diagnostic tests, and subjective impression of the usefulness of MR imaging were determined.

RESULTS

Seven hundred thirty-one of 840 pre- and post-MR imaging diagnoses agreed. Agreement was lowest for medial meniscal injuries (54 of 84). Significantly fewer meniscal injuries were suspected after MR imaging (P < .05). In 60 patients, the orthopedist changed at least one of the 10 potential diagnoses after MR imaging. Clinical diagnostic certainty increased by a mean of 14% for all diagnoses. The increase in diagnostic certainty was greatest for medial meniscal injuries (30%), followed by lateral meniscal injuries (21%). The proposed management changed in 41 patients, resulting in significantly fewer arthroscopic procedures (P < .01). The post-MR imaging management plans included 37% (27 of 73) fewer arthroscopic procedures.

CONCLUSION

MR imaging affects the diagnosis and management of acute knee injury by decreasing the number of arthroscopic procedures, improving clinician diagnostic certainty, and assisting in management decisions.

The efficacy of arthroscopy following total knee replacement

We evaluated the utility and safety of arthroscopy for diagnosing and treating symptoms in problematic total knee replacements. From 1988 to 1995, 40 arthroscopies were performed on 38 patients with an average age of 68.4 years. The average onset of symptoms post knee replacement was 33.7 months (range 1 month to 15 years), and the average duration of symptoms prior to arthroscopy was 15.6 months (range 1 month to 5 years). Presenting symptoms included pain in 73%, catching or soft tissue impingement in 35%, and stiffness in 20% of patients. Our protocol involves 24 hours of perioperative, intravenous antibiotics, and two or three routine arthroscopic portals. There were no arthroscopy-related complications or infections. Arthroscopy successfully diagnosed the etiology of the patient's symptoms in all but one case (97.5%). Operative diagnoses included impinging soft tissue under the patella consistent with the "clunk" syndrome (43%), impinging hypertrophic synovitis elsewhere in the knee (15%), impinging PCL stump (10%), prosthesis loosening or wear (10%), and arthrofibrosis (20%). Arthroscopic treatment consisted of removal of impinging tissue or loose body as indicated. Additionally, eight of the patients had a manipulation under anesthesia with an average improvement in flexion of 26.3 degrees postoperatively. At an average follow-up of 19.9 months, 27.5% of knees had developed recurrent symptoms. Two of these patients had repeat arthroscopy for recurrent impinging hypertrophic synovitis. The rates of successfully relieving symptoms without recurrence according to operative diagnosis were 82% for "clunks," 60% for other impinging synovium or soft tissue, and 63% for arthrofibrosis. Three patients underwent total knee revisions. Knees were rated at follow-up using the Knee Society rating system with patients divided according to functional category. The average Knee Society knee scores and function scores respectively were 93 and 92 for group A patients, 91 and 88 for group B patients, and 81 and 76 for group C patients. Arthroscopy successfully identified all cases of soft tissue impingement and prosthetic loosening or wear, and successfully treated 73% of patients without recurrence. There were no arthroscopy associated complications or infections. Thus, arthroscopy is a safe, effective tool for managing certain problematic knee replacements, especially "clunks," and may help to avoid revision or arthrotomy in some cases.

Total knee replacement in young, active patients. Long-term follow-up and functional outcome

We reviewed our experience with total knee arthroplasties performed between 1977 and 1992 in patients who were fifty-five years old or less to determine the appropriate management for younger patients who have severe osteoarthrosis. One hundred and fourteen knee replacements were performed in eighty-eight patients who were an average of fifty-one years old (range, twenty-two to fifty-five years old). All of the operations were performed by one of the two senior ones of us (J. N. I. or W. N. S.) with the use of cementing techniques. A posterior stabilized, posterior cruciate-substituting design was used for all but one replacement, for which a semiconstrained total condylar prosthesis was used. Six knees (four patients) were lost to follow-up. Follow-up data for the remaining 108 knees (eighty-four patients) were used to perform the survivorship analysis. One hundred and three unrevised knees (eighty patients) were available for clinical evaluation with the scoring systems of The Hospital for Special Surgery and the Knee Society at an average of eight years (range, three to eighteen years) postoperatively; thirty-six knees were followed for more than ten years. In addition, the activity levels of the patients were assessed with the activity score of Tegner and Lysholm. Radiographs were examined for evidence of loosening of the component. At the latest follow-up examination, the average knee score according to the system of The Hospital for Special Surgery had improved from 55 points preoperatively to 92 points. According to the system of the Knee Society, the average knee score was 94 points and the average functional score was 89 points. The result for all 103 knees was good or excellent according to the knee scores of The Hospital for Special Surgery and the Knee Society. Ninety-seven knees (94 per cent) had good or excellent function according to the functional score of the Knee Society. The average activity score of Tegner and, Lysholm improved from 1.3 points (range, 0 to 4 points) preoperatively to 3.5 points (range, 1 to 6 points) at the latest follow-up examination. All but two patients had improvement in the activity score postoperatively, and nineteen (24 per cent) of the eighty patients had an activity score of at least 5 points, indicating regular participation in activities such as tennis, skiing, bicycling, or strenuous farm or construction work. Nine (9 per cent) of the 103 knees had non-progressive tibial radiolucent lines. Two patients had a revision because of late infection, and one patient had revision of a well fixed tibial component because of wear of the polyethylene. In addition, three patellar components were revised for loosening, and one spacer was exchanged to treat instability. With failure defined as revision of either the femoral or the tibial component, the over-all rate of survival was 94 per cent at eighteen years. When the three patellar revisions were included in the failures, the survival rate was 90 per cent at eighteen years. When the exchange of the spacer was also included in the failures, the survival rate was 87 per cent at eighteen years. We consider arthroplasty with cementing of a posterior stabilized total knee prosthesis to be effective operative treatment with durable results for osteoarthrosis in younger patients when other, less invasive measures have failed. Within the average eight-year follow-up interval of this study, polyethylene wear, osteolysis, and loosening of the conforming posterior cruciate-substituting prosthesis were not major problems for these younger, active patients, although it is possible that this observation could change with an even longer duration of follow-up.

Two cell lines from bone marrow that differ in terms of collagen synthesis, osteogenic characteristics, and matrix mineralization

Two cloned cell lines were isolated from cultures of mouse bone-marrow cells. One of the lines, D1, exhibited osteogenic properties and synthesized type-I collagen (alpha 1)2 alpha 2. The second cell line, D2, was not osteogenic and produced a collagen homotrimer (alpha 1)3. Whereas the extracellular matrix of the D1 cell cultures contained striated collagen fibrils, presumably composed of type-I collagen, the homotrimer-producing D2 cells did not demonstrate striated collagen fibrils. Instead, they had thin filaments without detectable striations. Sodium ascorbate stimulated collagen synthesis at the transcriptional level in both the D1 and the D2 cells. The bone-producing characteristics of D1 in vitro included high levels of alkaline phosphatase, increased cyclic adenosine monophosphate on treatment with parathyroid hormone, and expression of osteocalcin mRNA. The D1 cells, unlike the D2 cells, produced a mineralized matrix in vitro. Mineralization in the cultures of the D1 cells occurred in nodules of increased cell density, which also contained the cells with the highest concentrations of collagen mRNA, as shown by in situ hybridization. When the D1 cells were implanted in a diffusion chamber in vivo, a mixture of both osteogenic and adipogenic tissues was formed. This indicates that the D1 cell line is derived from an early marrow stromal precursor that is multipotential.