Friday, April 22, 2011

NATURE MATERIALS | ARTICLE

Nanofibrous hollow microspheres self-assembled from star-shaped polymers as injectable cell carriers for knee repair

Nature Materials

10,

398–406

(2011)

doi:10.1038/nmat2999

Received: 19 December 2009
Accepted: 01 March 2011
Published online: 17 April 2011

To repair complexly shaped tissue defects, an injectable cell carrier is desirable to achieve an accurate fit and to minimize surgical intervention. However, the injectable carriers available at present have limitations, and are not used clinically for cartilage regeneration. Here, we report nanofibrous hollow microspheres self-assembled from star-shaped biodegradable polymers as an injectable cell carrier. The nanofibrous hollow microspheres, integrating the extracellular-matrix-mimicking architecture with a highly porous injectable form, were shown to efficiently accommodate cells and enhance cartilage regeneration, compared with control microspheres. The nanofibrous hollow microspheres also supported a significantly larger amount of, and higher-quality, cartilage regeneration than the chondrocytes-alone group in an ectopic implantation model. In a critical-size rabbit osteochondral defect-repair model, the nanofibrous hollow microspheres/chondrocytes group achieved substantially better cartilage repair than the chondrocytes-alone group that simulates the clinically available autologous chondrocyte implantation procedure. These results indicate that the nanofibrous hollow microspheres are an excellent injectable cell carrier for cartilage regeneration.

Figures at a glance

left

For further information:

http://www.nature.com/nmat/journal/v10/n5/abs/nmat2999.html

Thursday, April 7, 2011

SPORTS MEDICINE

Posted on the ORTHOSuperSite March 10, 2011

Better results seen with hamstring autografts than patellar tendon grafts 15 years after ACL reconstruction

SAN DIEGO — Patients who underwent ACL reconstruction with patellar tendon autograft displayed significantly worse outcomes at 15 years postoperative than those reconstructed with four-strandhamstring tendon, according to results of a study presented here.

Leo A. Pinczewski, MBBS, FRACS, presented the findings at the 2011 American Orthopaedic Society for Sports Medicine Specialty Day Meeting.

Pinczewski and colleagues compared the results of 90 consecutive patients with isolated ACL ruptures who underwent hamstring tendon repair with a cohort of 90 patients who had the same injury and underwent patellar tendon repair using the same surgical technique.

The investigators assessed the groups at 2, 5, 7, 10 and 15 years. These assessments included the IKDC Knee Ligament Evaluation, KT-1000, Lysholm Knee Score, kneeling pain, radiographic evaluation and other clinical outcomes.

“After 15 years, significant differences emerge,” Pinczewski said. At the 15-year mark, he noted that patients who received the patellar tendon graft displayed significantly worse outcomes than those who received hamstring tendon repair regarding radiologically-detectable osteoarthritis, motion loss, the single-leg hop test, participation in strenuous activity and kneeling pain.

No significant differences were reported between the groups regarding laxity and overall IKDC grade.

ACL graft rupture occurred in 16% of patients in the hamstring tendon group and 8% of patients in the patellar tendon group. In the study, these ruptures were associated with male patients and non-ideal tunnel position.

Pinczewski also noted that contralateral ACL rupture occurred in more patellar tendon patients than hamstring tendon patients (24% vs. 12%), and these occurrences were associated with patients younger than 18 years old.

For further information: http://www.orthosupersite.com/view.aspx?rid=81404

HIP

ORTHOPEDICS March 2011;34(3):186.

Arthroscopic Hip Surgery for the Treatment of Femoroacetabular Impingement

by J.W. Thomas Byrd, MD

In this issue of ORTHOPEDICS, Dr Byrd discusses the importance of patient selection in arthroscopic hip surgery and its use in adolescents and athletes.

In addition to being less invasive, what advantages exist for arthroscopy vs open treatment methods?

The obvious advantage of arthroscopy is that it is less invasive. However, the arthroscopic approach to femoroacetabular impingement is much more than just the technique. Arthroscopy precisely defines the secondary damage that accompanies femoroacetabular impingement and thus is part of the treatment algorithm for determining that bony correction of the impingement is necessary. Many patients may have impingement morphology without impingement pathology. What this means is that many people who have oddly shaped hips pursue long, active lifestyles and never develop problems. Keep in mind that impingement is not a cause of hip pain. Impingement is simply a morphologic condition that predisposes the joint to the secondary damage that then results in the accompanying symptoms.

Is there any single strong predictor of symptoms of femoroacetabular impingement?

Probably the strongest predictor for femoroacetabular impingement is simply maintaining an index of suspicion. When a young adult presents with hip joint pain, the most common lesion is damage to the acetabular labrum. However, it is not normal for the labrum to tear, even in the presence of highly physical activities, and the most likely underlying culprit is a component of femoroacetabular impingement. In dancers and groups where flexibility is a premium, dysplasia may be more common because individuals with dysplasia exhibit more mobility. This mobility may be an advantage, right up to the point that the labrum and other joint structures start to break down.

When is arthroscopy not a good option for the treatment of femoroacetabular impingement?

J.W. Thomas Byrd

On average, in the hands of a surgeon experienced with arthroscopic management of impingement, most cases can be treated by this method. Having said that, there are many circumstances where the open approach is still clearly the best. Cases that require a concomitant acetabular or proximal femoral osteotomy and some extreme cases of global overcoverage are performed open.

How important is patient selection in the management of femoroacetabular impingement arthroscopically?

Like many operations, patient selection is probably the most important factor in the success of the procedure. First, does the problem require surgery at all, and is it matched for an arthroscopic solution? Second, does the patient have reasonable expectations for the given severity of damage that is being addressed? Ultimately, the success of the procedure is determined by the level of patient satisfaction, and it is important that their expectations can be reasonably met. Lastly, the patient must be ready for the rehabilitation and recovery that is necessary for a successful outcome. I tell patients that surgery is the easy part; I will take care of that for them. It is the rehabilitation and recovery effort on their part that can take 4 months or longer.

What techniques, if any, have been developed to address femoroacetabular impingement and osteoarthritis in athletes?

Numerous techniques have been developed that aid in addressing femoroacetabular impingement and osteoarthritis in athletes. Our clinical assessment skills are getting better, and imaging technology is improving to detect the damage accompanying femoroacetabular impingement. In our experience, >90% of athletes and nonathletes alike already have grade III and grade IV articular damage at the time of arthroscopic intervention. This tells us that we are intervening late in the disease course. Earlier intervention would be preferable, although we have to be cautious about not recommending surgery in asymptomatic individuals. Instruments are available for reshaping the acetabulum and the femoral head to correct the impingement problem. The labrum has been found to have excellent healing capacity, and labral repair techniques have really blossomed. Our biggest challenge remains what to do about the articular surface. Microfracture has been a tried-and-true method, but it is still imperfect. Numerous articular cartilage restorative techniques remain in the works.

Is hip arthroscopy a safe procedure in adolescents with femoroacetabular impingement?

Impingement can first start to manifest itself in adolescence, shortly after skeletal maturity. This is especially true among athletes who are pushing their bodies beyond the diminished physiologic limits imposed by femoroacetabular impingement. Substantial secondary damage is sometimes encountered, even among teenagers. Arthroscopy is just as safe in this population as in mature adults. Of course, numerous precautions are necessary in those who have not yet reached skeletal maturity. The eventual outcome of impingement has usually not been fully determined yet, and any surgery must take into account the risk of altering skeletal growth.

Is there any way to predict the future occurrence of osteoarthritis following hip arthroscopy?

Although no precise statistical data exists, the risk of future osteoarthritis is probably most closely tied to the severity of articular damage at the time of arthroscopic intervention. Thus, earlier detection and intervention still seems preferable once someone’s problem has declared itself.

What is on the horizon for the arthroscopic treatment of femoroacetabular impingement?

The 2 biggest technical challenges with treatment of impingement are the precision with which the bony correction is performed and

knowing exactly what is the right amount of bone to remove. Computer assistance in assessing the morphology of the impingement problem and intraoperative navigation for its correction are on the immediate horizon. Presently, we are forced to make these surgical corrections freehand, and no one knows exactly the precise amount of bone to remove. Computer assistance is close in the future. We do not perform joint replacement surgery without preoperative templates and intraoperative jigs. In the near future, computer assessment will be our templating, and computer navigation will be our intraoperative jigs. It will not be long before we reflect back on these days when we performed this freehand. We are doing okay, but we can and need to do much better.

For further information: http://www.orthosupersite.com/view.aspx?rid=80983

FOOT AND ANKLE

ORTHOPEDICS April 2011;34(4):272.

Ankle Fusion Stability: A Biomechanical Comparison of External Versus Internal Fixation

by Justin R. Hoover, MD; Robert D. Santrock, MD; William C. James, MD

Abstract

This biomechanical study compares bimalleolar external fixation to conventional crossed-screw construct in terms of stability and compression for ankle arthrodesis. The goals of the study were to determine which construct is more stable with bending and torsional forces, and to determine which construct achieves more compression.

Fourth-generation bone composite tibia and talocalcaneal models were made to 50th percentile anatomic specifications. Fourteen ankle fusion constructs were created with bimalleolar external fixators and 14 with crossed-screw constructs. Ultimate bend, torque, and compression testing were completed on the external fixator and crossed-screw constructs using a multidirectional Materials Testing Machine (MTS Systems Corp, Eden Prairie, Minnesota). Ultimate bend testing revealed a statistically significant difference (P=.0022) with the mean peak load to failure for the external fixator constructs of 973.2 N compared to 612.5 N for the crossed-screw constructs. Ultimate torque testing revealed the mean peak torque to failure for the external fixator construct was 80.2 Nm and 28.1 Nm for the crossed-screw construct, also a statistically significant difference (P=.0001). The compression testing yielded no statistically significant difference (P=.9268) between the average failure force of the external fixator construct (81.6 kg) and the crossed-screw construct (81.2 kg).

With increased stiffness in both bending and torsion and comparable compressive strengths, bimalleolar external fixation is an excellent option for tibiotalar ankle arthrodesis.

Ankle arthrodesis has historically been the mainstay of surgical treatment of end-stage ankle arthrosis. Various constructs have been described to create a stable tibiotalar fusion. Open tibiotalar joint preparation with internal crossed-screw fixation is widely used. However, other options are available, and less invasive procedures are particularly useful in patients with a history of infection, poor soft tissue quality, or poor wound-healing capabilities. Open crossed screw construct, plating, intramedullary nail, and external fixation to obtain fusion are described in the literature, and many biomechanical studies have been performed.^1-13 The basic premise remains the same: no matter what type of fixation is chosen, stability and compression are needed for successful fusion. It is for this reason that the biomechanical properties of different techniques and constructs continue to be investigated with the goals of improving stability and, in turn, patient outcomes.

In this study, we compared traditional crossed-screw fixation to bimalleolar external fixation in bending, torsion, and compression. Bimalleolar external fixation was originally described by Charnley in 1951.⁵Since that time, use of these constructs has been relatively limited. Recently, external fixation has gained interest due to the perceived stability. Our hypothesis for this study was that bimalleolar external fixation is superior to crossed-screw technique in bending strength, torsional strength, and compression.

Materials and Methods

Fourth-generation bone composite replicated tibia and talocalcaneal constructs were made to 50th percentile human anatomic specifications.^14,15 These constructs have been shown to be comparable to natural bone in terms of their biomechanical properties.¹⁴ Each construct was cut precisely to replicate the average human ankle and foot size, therefore giving the appropriate lever arms during mechanical testing. The tibial construct was 40×40×180 mm. The talocalcaneal foot construct block was 40×60×173 mm with a trapezoid talar dome 10 mm in height and a tibiotalar contact surface of 40×25 mm.

A total of 28 constructs were built for mechanical testing. Fourteen external fixation constructs were created using Sidekick Stealth bimalleolar external fixators (Wright Medical Technology, Inc, Arlington, Tennessee). Fourteen conventional crossed-screw fixation constructs were created using 6.5-mm Darco partially threaded cannulated screws (Wright Medical Technology, Inc).

To create the external fixator constructs, four 4.0×300-mm transfixing external fixator pins were inserted in standard fashion in the constructs’ talar neck, calcaneus, and proximal and distal tibia. The talar neck pin was placed 25 mm plantar to the talar dome surface and 15 mm anterior. The calcaneal pin was placed 15 mm proximal to the plantar surface and 15 mm anterior to the posterior aspect of the calcaneal block. The distal tibial pin was placed 30 mm proximal to the construct plafond and 12 mm posterior to the anterior tibial crest. The proximal tibial pin was placed 90 mm proximal to the construct plafond and 20 mm posterior to the anterior tibial crest. The medial and lateral Sidekick Stealth external fixator frames were then placed 32 mm from the medial and lateral edge of the composite bone (Figure 1).


Figure 1: Bimalleolar external fixator construct. Figure 1: Bimalleolar external fixator construct.

The internal fixation crossed-screw constructs were built by predrilling the tibial and talocalcaneal constructs with a 4.4-mm drill bit. This was followed by countersinking the tibial composite bone. Two 6.5×70-mm Darco partially threaded headed screws were placed in standard crossed screw construct from the medial and lateral side of the tibia construct into the talocalcaneal construct (Figure 2).

Ultimate Bend Testing

Four external fixator and 4 crossed-screw constructs were fashioned in the manner outlined above. The tibial component was secured to the base plate box of the multidirectional Materials Testing Machine (MTS machine; MTS Systems Corp, Eden Prairie, Minnesota). The actuator was placed on the plantar surface of the talocalcaneal construct 12.7 mm from the distal end. The MTS machine actuator applied a load at 1 mm per second with data acquisition at 50 Hz until failure. Data was recorded in newtons of force. Failure was defined as a drop in the load (caused by composite fracture, screw pullout, or brace plate fracture).

Ultimate Torque Testing

Four external fixator and 4 crossed-screw constructs were fashioned in the manner outlined above. The tibial component was secured to the base plate box of the multidirectional MTS machine. The actuator was placed on the plantar surface of the talocalcaneal construct in line with the center of the talar dome. The MTS machine actuator applied a load of 1° per second with data acquisition at 25 Hz until failure. Data was recorded in newton-meters. Failure was defined as a drop in the load (caused by composite fracture, screw pullout, or brace plate fracture).

Compression Testing

Six external fixator and 6 crossed-screw constructs were fashioned in the manner outlined above with the exception of placing a 6.35-mm Load Washer Load Cell (Interface, Inc, Scottsdale, Arizona) and a 76.2×76.2×0.8-mm aluminum plate between the tibial and talocalcaneal composite bone (Figure 3). The external fixator talocalcaneal pins were tightened in a static position both medially and laterally. The tibial component was advanced proximally by turning each of the 4 nuts one-quarter turn. Measurements at each one-quarter turn were made in kilograms of force. This was completed until failure. The crossed-screw compression was measured similarly. The crossed screws were set when the underside of the screw head contacted the composite bone material. Once this contact was made, each screw was tightened one-quarter turn, and kilograms of force measurements were made after each one-quarter turn until failure. The number of turns and kilograms of force were recorded. Failure was defined as fracture of the composite bone material in the crossed-screw construct and damage to the articulating bar threads leading to inability to advance the nuts on the medial and lateral braces in the external fixator group.

Figure 3: Compression testing model with transducer.

It is to be noted that only 5 external fixator constructs were analyzed, as external fixator sample 1 was loaded without the aluminum plate and therefore was not equivalent to the other constructs and was eliminated from the data. The aluminum plate was necessary to insert because the ring transducer embedded into the composite bone when compressed.

Statistical Analysis

The mean, maximum, minimum, and standard deviations of each parameter at failure were calculated. Student t test was used to compare the external fixation group to the crossed-screw construct group. Statistical significance level was set at P<.05.

Results

The mean peak load to failure for dorsiflexion for the external fixator was 973.2±109.5 N and for the crossed-screw construct was 612.5±89.2 N, which was a statistically significant difference (P=.0022) (Table 1, Figure 4).

Table 1: Ultimate Bend (Dorsiflexion) Peak Load

Figure 4: Peak load (n=4).

The mean bending stiffness of the composite tibiotalar joint for each condition is shown in Table 2. The Stealth external fixator yielded a bending stiffness of 34,373±2017 Nm, and the Darco crossed-screw construct was 26,285±1416 Nm, which is a statistically significant difference (P=.0006) (Table 2, Figure 5).

Table 2: Bending Stiffness

Figure 5: Bending stiffness (n=4).

Ultimate torque testing revealed the mean peak torque to failure for the external fixator construct was 80.2±11.5 Nm and the crossed-screw construct was 28.1±3.0 Nm. This was a statistically significant difference (P=.0001) (Table 3, Figure 6).

Table 3: Peak Torque

Figure 6: Mean peak torque (n=4).

The mean torsional stiffness for the external fixator construct was 3.09±0.10 Nm/degree. The crossed-screw construct mean torsional stiffness was 1.36±1.04 Nm/degree. This was a statistically significant difference using the t test (P=.0324) (Table 4, Figure 7).

Table 4: Torsional (External Rotation) Stiffness

Figure 7: Torsional stiffness (n=4).

Compression testing yielded no statistically significant difference (P=.9268) between the average failure force of the external fixation (81.6 kg) and the crossed screws (81.2 kg). The external fixator failure mode was the nut would not advance further due to damage of the articulating bar threads. Four turns of each nut was the average number of turns to failure. The failure mode for all Darco crossed-screw constructs was fracture of the composite bone. The average number of screw turns was 1.5 turns after the screw was seated (Table 5).

Table 5: Compression Testing

Discussion

Ankle arthrodesis is a valuable procedure for end-stage ankle arthrosis. Multiple techniques have been described, including internal and external fixation. Numerous clinical studies have shown internal crossed screw construct as advantageous due to high rates of fusion, decreased rates of infection, and improved patient comfort.^1-13 However, in many cases external fixation may be a more appropriate means of facilitating fusion. Ring external fixators have been shown to be a viable option to establish fusion and is particularly useful in cases of past infection, poor wound-healing capabilities, or decreased bone stock.¹⁰ To our knowledge, no study has compared a compression arthrodesis technique using bimalleolar external fixation to crossed screws. Our hypothesis was that bimalleolar external fixation is a more rigid construct with regard to bending strength (dorsiflexion), torsional strength, and compression than crossed screws.

Our results revealed statistically significant differences in both bending forces (P=.0022) and torsional forces (P=.0001), showing that external fixation is more rigid than crossed screws. No statistical significance was seen with regard to compression.

Our study protocol had several limitations, including the use of fourth-generation bone composite, not accounting for subtalar joint involvement, space-occupying use of the load cell ring transducer, effects of musculature and ligaments, and unidirectional force measurements performed on the MTS machine at nonphysiologic rates. Our plans include performing a cadaveric study with multidirectional testing using a bimalleolar external fixator and crossed screws. These anatomic specimens will allow us to take into account the subtalar joint. Additionally, we would like to use less invasive devices to assess compression.

Conclusion

Bimalleolar external fixator is a more rigid construct in both bending and torsion as compared to conventional crossed screws. There was no significant difference between the 2 methods with regard to compression. However, with increased stiffness in both bending and torsion and comparable compressive strengths, a bimalleolar external fixator is an excellent option for tibiotalar ankle arthrodesis in the correct clinical setting. Clinical indications would include patients with a history of infection or poor soft tissue quality.⁶ In our practice, it is also useful for arthroscopic-assisted ankle fusions due to its minimally invasive nature; it has become our primary mode of fixation for these fusions. Biomechanical testing predicts that it has a low probability of failure due to rigidity of the construct. External fixation was found to be more rigid than a traditional lag-screw technique. These findings may extrapolate into increased fusion rate and earlier or immediate weight bearing in patients undergoing ankle arthrodesis. This would potentially reduce the associated morbidity of extended nonweight bearing while increasing patient satisfaction.

For further information: http://www.orthosupersite.com/view.aspx?rid=81555

ORTHOPEDICS April 2011;34(4):276.

Posterior Reattachment of a Radial Tear in the Posterior Root of the Medial Meniscus

by Kyung Wook Nha, MD; Kook Hyun Wang, MD; Gautam M. Shetty, MD; Chang Soo Lee, MD; Jong In Kim, MD

The new posterior vertical mattress suture technique is technically easier to perform and provides more secure fixation than the arthroscopic simple or horizontal stitch techniques and may contribute to restoring function of the medial meniscus.

Cover illustration © Scott Holladay

The meniscus is known to have a role in shock absorption and dispersing load transmission, thereby protecting and enhancing stability of the knee joint. A radial tear at the posterior root of the medial meniscus is not uncommon. A root tear has been defined as a radial tear that occurs within 1 cm of the posterior horn insertion.¹ Recent studies have shown a relatively high incidence of complete posterior medial meniscus root tear, especially in east Asia.² A complete posterior medial meniscus root tear leads to a loss of hoop tension, resulting in a reduction of contact surface, thereby increasing contact pressure within the joint and leading to accelerated degenerative changes.³

Several reports have concluded that radial tears of the meniscus have a clinically different outcome when compared to other types of meniscal tears.⁴ Meniscectomy in these patients does not seem to prevent acceleration of osteoarthritis. Recently, an arthroscopic pullout suture technique has been described in the literature as a mode of surgical treatment for complete posterior medial meniscus root tear.^5,6 However, in this technique, a simple suture is placed along the direction of the circumferential collagen fibers within the meniscus, and hence is liable to failure when increased tensile forces are present.⁴ This article describes a more secure fixation method to restore the function of the meniscus by posterior reattachment using a vertical mattress suture.