Surgical treatment of knee osteoarthritis focusing on the patellofemoral joint

Surgical management of the osteoarthritic knee joint consists of osteotomies such as a high tibial osteotomy (HTO), uni-compartmental knee arthroplasty (UKA), and total knee arthroplasty (TKA). These surgeries mainly treat the tibiofemoral joint but can also have an impact on the patellofemoral (PF) joint. These changes in PF joint can affect the surgical outcome.Current Concepts: PF joint problems are relative contraindications in UKA. However, recent studies have reported that these problems do not markedly affect the result of UKA. During HTO, the patella height and tracking can change, affecting the PF joint problem. The effect of the PF joint can be minimized through various methods of closing wedge HTO or modified opening wedge (OW) HTO, such as retro-tubercular biplanar OWHTO. However, this method is controversial regarding its impact on clinical outcomes. In TKA, pain caused by PF joint problems can be reduced using techniques such as patella resurfacing, patelloplasty, and denervation; however, there is no clear consensus.Discussion and Conclusion: The surgical treatment of degenerative knee osteoarthritis has an impact on the PF joint, which can affect the outcome of surgery and vice versa. However, these impacts only occasionally cause clinical difference. Conclusively, these surgeries should be done by considering the PF joint because changes in the joint can affect the surgical outcome.

Changes in hamstring strength after anterior cruciate ligament reconstruction with hamstring autograft and posterior cruciate ligament reconstruction with tibialis allograft

Methods@#Isokinetic strengths of the quadriceps and hamstring muscles and endurances were compared between a group of 20 patients undergoing PCLR using a tibialis anterior allograft and a 1:2 matched control group of 40 patients undergoing ACLR using a hamstring autograft at 2 years after the operations. Clinical results were also compared using stability tests and the Lysholm and the International Knee Documentation Committee scores. @*Results@#At 2 years after the operations, the torque deficit of the hamstring muscle in the involved leg compared to the uninvolved leg at both 60°/s and 120°/s was greater in the PCLR group than in the ACLR group (60°/s, 21.8 ± 14.0% versus 1.9 ± 23.9%, P = 0.0171; 120°/s, 15.3 ± 13.7% versus −0.7 ± 17.4%, P = 0.012, respectively). The peak torque of the hamstring muscle at 120°/s was significantly lower in the involved leg than in the uninvolved leg only in the PCLR group (71.3 ± 31.9 N·m versus 81.9 ± 27.8 N·m, P = 0.005). There was no significant difference in the clinical results between the groups except for a side-to-side difference in the tibial translation on Telos stress radiographs. @*Conclusion@#The strength of the hamstring of the PCLR leg with allograft was significantly weaker than that of the unoperated leg after 2 years, whereas that of the ACLR leg with hamstring autograft maintained a similar level of strength compared to that of the uninvolved leg.Level of evidence: Level III, case–control study.

Effectiveness of iron supplementation in the perioperative management of total knee arthroplasty: a systematic review

Materials and methods@#A rigorous and systematic approach was used and each of the selected studies was evaluated for methodological quality. Data about study design, total number of cases enrolled, iron administration method, timing, and dose were extracted. Change in hemoglobin and transfusion rates were extracted to evaluate the effectiveness of iron supplementation. @*Results@#Eleven studies were included in the final analysis. Most of studies reported that hemoglobin change between iron and control group did not show any difference. Only one study reported that iron supplementation could reduce the decrease in hemoglobin. However, transfusion rate showed a decrease in the iron supplementation group compared with the control group. There was no clear consensus on the optimum timing and dose of iron supplementation and intravenously administered iron was more effective than orally administered iron, especially in anemic patients. @*Conclusion@#Iron supplementation is not clear as a way to raise hemoglobin levels after TKA, but an effective treatment for lowering transfusion rate, especially in patients with anemia. We could not determine the optimal timing and dose of the iron. Intravenously administered iron was similar to, or better than, orally administered iron for improving hemoglobin levels and transfusion rate.

Is there an optimal age for total knee arthroplasty?: A systematic review

Purpose@#The purpose of this systematic review was to elucidate the optimal age for patients undergoing total knee arthroplasty (TKA), to optimize the balance between the benefits and risks by analyzing patient-reported outcome measurements (PROM), revision rate, and mortality according to age. @*Materials and methods@#A rigorous and systematic approach was used and each of the selected studies was evaluated for methodological quality. Data were extracted according to the following: study design, patients enrolled, patient age at the time of surgery, follow-up period, PROM, revision rate, and mortality. @*Results@#Thirty-nine articles were included in the final analysis. The results were inconsistent in the PROM analysis, but there was consensus that PROM were good in patients in their 70s . In the revision rate analysis, there was consensus that the revision rate tends to increase in TKA in younger patients, but no significant difference was observed in patients > 70 years of age. In the mortality analysis, there was consensus that the mortality was not significantly different in patients < 80 years of age, but tended to increase with age. @*Conclusion@#This systematic review shows that the PROM were good when TKA was performed in patients between 70 and 80 years of age; the best PROM could be achieved around 70 years of age, and no significant difference in the revision or mortality rates was observed between 70 and 80 years of age; however, mortality tended to increase with age. Therefore, the early 70s could be recommended as an optimal age to undergo TKA.

Effectiveness of iron supplementation in the perioperative management of total knee arthroplasty: a systematic review

Materials and methods@#A rigorous and systematic approach was used and each of the selected studies was evaluated for methodological quality. Data about study design, total number of cases enrolled, iron administration method, timing, and dose were extracted. Change in hemoglobin and transfusion rates were extracted to evaluate the effectiveness of iron supplementation. @*Results@#Eleven studies were included in the final analysis. Most of studies reported that hemoglobin change between iron and control group did not show any difference. Only one study reported that iron supplementation could reduce the decrease in hemoglobin. However, transfusion rate showed a decrease in the iron supplementation group compared with the control group. There was no clear consensus on the optimum timing and dose of iron supplementation and intravenously administered iron was more effective than orally administered iron, especially in anemic patients. @*Conclusion@#Iron supplementation is not clear as a way to raise hemoglobin levels after TKA, but an effective treatment for lowering transfusion rate, especially in patients with anemia. We could not determine the optimal timing and dose of the iron. Intravenously administered iron was similar to, or better than, orally administered iron for improving hemoglobin levels and transfusion rate.

Is there an optimal age for total knee arthroplasty?: A systematic review

Purpose@#The purpose of this systematic review was to elucidate the optimal age for patients undergoing total knee arthroplasty (TKA), to optimize the balance between the benefits and risks by analyzing patient-reported outcome measurements (PROM), revision rate, and mortality according to age. @*Materials and methods@#A rigorous and systematic approach was used and each of the selected studies was evaluated for methodological quality. Data were extracted according to the following: study design, patients enrolled, patient age at the time of surgery, follow-up period, PROM, revision rate, and mortality. @*Results@#Thirty-nine articles were included in the final analysis. The results were inconsistent in the PROM analysis, but there was consensus that PROM were good in patients in their 70s . In the revision rate analysis, there was consensus that the revision rate tends to increase in TKA in younger patients, but no significant difference was observed in patients > 70 years of age. In the mortality analysis, there was consensus that the mortality was not significantly different in patients < 80 years of age, but tended to increase with age. @*Conclusion@#This systematic review shows that the PROM were good when TKA was performed in patients between 70 and 80 years of age; the best PROM could be achieved around 70 years of age, and no significant difference in the revision or mortality rates was observed between 70 and 80 years of age; however, mortality tended to increase with age. Therefore, the early 70s could be recommended as an optimal age to undergo TKA.

Disparity between Preoperative Target Correction Amount and Postoperative Correction Amount in Open Wedge High Tibial Osteotomy

PURPOSE: The purpose of this study was to evaluate the disparity between the preoperative target correction amount and the postoperative correction amount in open wedge high tibial osteotomy (OWHTO) in patients divided according to the planned osteotomy gap. MATERIALS AND METHODS: Seventy-two patients were divided into two groups (group 1 with the planned opening gap lager than the mean opening gap length of total patients and group 2 with a smaller opening gap). The opening gap was determined according to the target weight bearing line (WBL) ratio on the preoperative whole leg radiograph. Absolute and relative values of the disparity between the target and postoperative WBL ratios were compared between groups in order to clarify whether the disparity was deviated toward over- or under-correction. RESULTS: The absolute value of disparity between the target and postoperative WBL ratios in group 1 was significantly larger than that in group 2 (6.01%±5.68% vs. 3.32%±3.38%; p=0.02). However, there was no statistically significant difference in relative values between groups (p=0.54). CONCLUSIONS: The postoperative WBL ratio after OWHTO was different from the preoperative target WBL ratio if the planned osteotomy gap was large. This mismatch was not deviated toward one side, either over- or under-correction.

Preoperative Varus-Valgus Stress Angle Difference Is Valuable for Predicting the Extent of Medial Release in Varus Deformity during Total Knee Arthroplasty

PURPOSE: The purpose of this study was to compare the predictive value of the valgus stress angle (SA), varus SA and varus-valgus SA difference (VVD) in predicting the degree of medial release in varus deformity during total knee arthroplasty (TKA). MATERIALS AND METHODS: One hundred eight TKAs (78 patients), which were performed in primary osteoarthritis with varus knee deformity, were retrospectively classified into three groups according to the degree of medial release (group A, mild release; group B, moderate release; and group C, severe release). Medical charts were reviewed, and long weight bearing standing anteroposterior radiographs and varus-valgus stress radiographs were evaluated. RESULTS: The valgus SA was significantly different between group A and B and between group A and C. However, it was not significantly different between group B and C. The varus SA was significantly different between group B and C and between group A and C. However, it was not significantly different between group A and B. The VVD was significantly different in all intergroup comparisons. CONCLUSIONS: Evaluation of the VVD is more valuable in predicting the degree of medial release in TKA performed in varus knee deformity than evaluation of the simple valgus and varus SA.

Analysis of Mechanical Loading after Anatomic Anterior Cruciate Ligament Reconstruction Using Combined Single-Photon Emission Computerized Tomography and Conventional Computerized Tomography

PURPOSE: This study was to evaluate changes of the mechanical loading pattern after anatomic anterior cruciate ligament (ACL) reconstruction by analyzing uptake patterns using combined single-photon emission computerized tomography and conventional computerized tomography (SPECT/CT). MATERIALS AND METHODS: On SPECT/CT, high signal intensity of the articular surface which shows biological activity and mean increase of mechanical loading was compared with that of the tibiofemoral shaft as a comparative signal. The proportion of positive signals was evaluated in all compartments of the operated knee. Analysis was performed according to combined injury. RESULTS: A relatively high proportion of positive signals was detected in the posterior zone of the lateral tibial plateau (23.5%) and trochlear groove (23.5%) although increased signal intensity was detected in all compartments. There was no statistical difference depending on the presence of combined injury and between single-bundle and double-bundle ACL reconstruction. CONCLUSIONS: Following anatomic ACL reconstruction, higher signal intensity was detected, particularly in the posterior part of the lateral tibial plateau and trochlear groove. Close observation for further signal changes or osteoarthritic changes would be required even if there was no combined injury and anatomic reconstruction was performed.

The mechanism and cause of anterior cruciate ligament tear in the Korean military environment

PURPOSE@#Anterior cruciate ligament (ACL) injury is very common but few studies have analyzed the injury mechanism and cause of ACL tear in a specific environment such as a military institution. The purpose of this study was to analyze the injury mechanism and cause of ACL injury in the military environment. Additionally, this study could provide outcomes that may aid future studies on prevention of ACL injury in military personnel.@*MATERIALS AND METHODS@#This study retrospectively analyzed 168 patients who sustained ACL tear while in military service and underwent ACL reconstruction surgery in a military hospital. Analysis of the injury mechanism and the cause was evaluated by analyzing the medical records. Knee magnetic resonance imaging analysis was also conducted for further evaluation of associated injury.@*RESULTS@#The majority of ACL injuries in the military environment occurred through non-contact injury. Changing direction (46.4%) was the most common lower-leg position, followed by landing with the knee in a valgus position (26.8%). The activity undertaken at the time of injury was exercise in 76.2% of cases and military training/daily activities in 23.8% of cases. The incidence of ACL injury was higher in the soldier compared to the officer group during exercise (P = 0.017). Soccer was the most common activity at the time of injury (54.1%), followed by military training/daily activities, futsal, and basketball. The most common injury time was between 30 and 60 min after the start of exercise. Commonly associated injury sites were the medial meniscus and the medial collateral ligament.@*CONCLUSIONS@#The main mechanism of ACL injury occurring in the military environment was non-contact injury, especially on changing the direction of the lower leg. Soccer was the most frequent activity at the time of the injury. These findings suggested that preventive strategies against ACL injury in the military environment could effectively reduce the incidence of ACL injury.

Magnetic Resonance Imaging and Clinical Results of Outside-in Anterior Cruciate Ligament Reconstruction: A Comparison of Fixed- and Adjustable-Length Loop Cortical Fixation

BACKGROUND: Cortical suspensory femoral fixation is commonly performed for graft fixation to the femur in anterior cruciate ligament (ACL) reconstruction using hamstring tendons. The purpose of this study was to compare graft healing in the femoral tunnel, implant-related failure, and clinical results between fixed- and adjustable-length loop devices in outside-in ACL reconstruction. METHODS: A total of 109 patients who underwent ACL reconstruction using the outside-in technique from December 2010 to July 2014 were included. For femoral graft fixation, a fixed-length loop device was used in 48 patients (fixed-loop group) and an adjustable-length loop device was used in 61 patients (adjustable-loop group). For evaluation of graft healing in the femoral tunnel, magnetic resonance imaging was performed at postoperative 6 months and the signal-to-noise ratios (SNRs) of the tendon graft and tendon-bone interface in the femoral bone tunnel were evaluated. The presence of synovial fluid was evaluated to determine loop lengthening at the femoral tunnel exit. Clinical results assessed using International Knee Documentation Committee score, Tegner-Lysholm Knee Scoring scale, and knee instability tests were compared between groups. RESULTS: The SNRs of the tendon graft and tendon-bone interface were not statistically different between groups. The presence of synovial fluid at the femoral exit showed no statistical difference between groups. Clinical results were not significantly different between groups. CONCLUSIONS: The adjustable-length loop device provided comparable graft healing, implant-related failure, and clinical results with the fixed-length loop device, allowing adaptation of the graft to the different tunnel lengths. Therefore, it could be effectively used with an adjustment according to the femoral tunnel length.

Does Coronal Knee and Ankle Alignment Affect Recurrence of the Varus Deformity after High Tibial Osteotomy?

PURPOSE: The purpose of this study was to evaluate changes in the coronal alignment of the knee and ankle joints after open wedge high tibial osteotomy (OWHTO) to determine factors related to the recurrence (R) of the varus deformity by serial analysis. MATERIALS AND METHODS: Sixty-four OWHTOs were enrolled in this study. The weight bearing line (WBL) ratio, joint line convergence angle (JLCA), knee joint inclination, mechanical axis-tibial plateau angle, talar inclination (TI), and distal tibia articular angle (DTAA) were serially assessed. Serial correlation analysis between all parameters was performed. Patients were divided into R group and no recurrence (NR) group according to the WBL ratio (55%) at postoperative one year. RESULTS: The preoperative WBL ratio showed significantly negative correlation with serial changes of JLCA, TI, and DTAA (p < 0.05). The JLCA, TI, and DTAA as well as WBL ratio showed a significantly larger degree of varus alignment in the R group than in NR group at postoperative 6 weeks and 1 year after OWHTO (p < 0.05). CONCLUSIONS: Sufficient correction of the WBL and restoration of the JLCA during OWHTO are essential to prevention of the R of varus deformity after the surgery because they are the only modifiable factors during surgery. LEVEL OF EVIDENCE: IV, Case series

Two-Stage Reimplantation in Infected Total Knee Arthroplasty

Two-stage reimplantation is considered the gold standard for the management of periprosthetic joint infection. The first stage involves the removal of the prosthesis, followed by extensive debridement of all nonviable tissues, synovectomy, irrigation, and reaming of the medullary canals. Once the joint has been prepared, antibiotic-impregnated cement beads and/or spacer are inserted. Antibiotic-impregnated spacers are now more commonly used, and an increasing number of orthopaedic surgeons are using articulating spacers if indicated. Antibiotics are then prescribed to the patient based on the sensitivities of the infecting organism. The duration of systemic antibiotic use is decreasing, and short courses of antibiotic therapy have been shown to be as efficacious as prolonged therapy between the first and second stages. The second stage of the procedure involves removal of the antibiotic-impregnated cement beads and/or spacer, repeat irrigation and debridement, and final reconstruction with revision components. While two-stage reimplantation was considered the gold standard in many parts of the world, recent studies have demonstrated that it is associated with a considerable failure rate. This may be due to the lack of accurate diagnostic tools for infection eradication, and future investigation of risk factors for failure of the two-stage reimplantation should be conducted.

Comprehensive Analysis of Pain Management after Total Knee Arthroplasty

Total knee arthroplasty (TKA) has been much improved recently and it is regarded as one of the most common and successful surgical procedures that provides pain relief and improves function in patients with severe knee arthritis. However, recent studies have reported that 15%–20% of patients are not satisfied after TKA without evident clinical or radiological findings and the most common causes of patient dissatisfaction include residual pain and limited function. The evaluation and treatment of painful TKA relies on a thorough understanding of the origin by careful evaluation, and a systematic approach is essential to efficiently and effectively resolve the pain. Periarticular injections (PAIs) and nerve blocks are gaining popularity because they are associated with less side effects than systemic regimens. The analgesic efficacy and safety of PAI compared with nerve blocks for postoperative pain management still remain controversial. Therefore, more study is needed to determine if any changes in the regimen of the injection or technique could provide added benefit to long-term functional improvement beyond the perioperative period.

Arthroscopic Control for Safe and Secure Seating of Suspensory Devices for Femoral Fixation in Anterior Cruciate Ligament Reconstruction Using Three Different Techniques

PURPOSE: The purpose of this study was to evaluate the efficacy of our technique that allows direct visualization of seating of suspensory devices in anterior cruciate ligament (ACL) reconstruction. MATERIALS AND METHODS: Three different suspensory devices (TightRope RT, RetroButton, and EndoButton) were used in ACL reconstruction using 3 different techniques (outside-in, anteromedial [AM] portal, and transtibial techniques). Positioning of a guiding material and seating pattern of the suspensory devices were evaluated according to the surgical technique and suspensory device used. RESULTS: On the transtibial technique, 21 of total 26 cases (81%) of single bundle reconstructions and 22 of total 22 cases (100%) of double bundle reconstructions required superolateral capsulotomy where buttons were found in 21 of total 21 cases (100%) and 17 of 22 cases (77%), respectively. On the AM portal technique, all patients required capsulotomy and the button was found in only 18 of total 32 cases (56%) even after capsulotomy. On the outside-in technique, all patients required capsulotomy and the button was found in 86 of total 86 cases (100%). CONCLUSIONS: Our technique for direct visualization of seating of the suspensory devices was more effective in outside-in and single bundle transtibial ACL reconstruction. However, it was less effective in double bundle transtibial and AM portal ACL reconstructions.

Golf-related Spine and Lower Extremity Injury / 대한스포츠의학회지

Golf is a popular worldwide sport played regardless of skill level, age, and sex. This characteristic is a major part of appeal. However, the golf swing involves a large range of motion and large forces of whole body and it is associated with a significant number of injuries. Lower back and upper extremity has similarly high injury incidence and followed by lower extremity. Knee, especially anterior cruciate ligament, can be serious in lower extremity injury. Poor swing mechanics and overuse are frequently related. However, injuries are also sustained from hitting the ground or being hit by a golf ball or club.

The SPECT/CT Evaluation of Compartmental Changes after Open Wedge High Tibial Osteotomy

PURPOSE: The purpose of this study was to evaluate compartmental changes using combined single-photon emission computerized tomography and conventional computerized tomography (SPECT/CT) after open wedge high tibial osteotomy (OWHTO) for providing clinical guidance for proper correction. MATERIALS AND METHODS: Analysis was performed using SPECT/CT from around 1 year after surgery on 22 patients who underwent OWHTO. Postoperative mechanical axis was measured and classified into 3 groups: group I (varus), group II (0°–3° valgus), and group III (>3° valgus). Patella location was evaluated using Blackburne-Peel (BP) ratio. On SPECT/CT, the knee joint was divided into medial, lateral, and patellofemoral compartments and the brighter signal was marked as a positive signal. RESULTS: Increased signal activity in the medial compartment was observed in 12 cases. No correlation was observed between postoperative mechanical axis and medial signal increase. Lateral increased signal activity was observed in 3 cases, and as valgus degree increased, lateral compartment’s signal activity increased. Increased signal activity of the patellofemoral joint was observed in 7 cases, and significant correlation was observed between changes in BP ratio and increased signal activity. CONCLUSIONS: For the treatment of medial osteoarthritis, OWHTO requires overcorrection that does not exceed 3 valgus. In addition, the possibility of a patellofemoral joint problem after OWHTO should be kept in mind.

Posterior Shift of Contact Point between Femoral Component and Polyethylene in the LCS Rotating Platform Implant under Weight Bearing Condition

PURPOSE: To analyze the contact mechanics of the femoral component and polyethylene of the Low Contact Stress rotating platform (LCS-RP) in nonweight bearing and weight bearing conditions using full flexion lateral radiographs. MATERIALS AND METHODS: From May 2009 to December 2013, 58 knees in 41 patients diagnosed with osteoarthritis and treated with total knee arthroplasty (TKA) were included in this study. TKA was performed using an LCS-RP knee prosthesis. Full flexion lateral radiographs in both weight bearing and nonweight bearing condition were taken at least one month postoperatively (average, 28.8 months). Translation of femoral component was determined by the contact point between the femoral component and polyethylene. Maximum flexion was measured as the angle between the lines drawn at the midpoint of the femur and tibia. RESULTS: Posterior shift of the contact point in LCS-RP TKA was observed under weight bearing condition, which resulted in deeper flexion compared to LCS-RP TKA under nonweight bearing condition. CONCLUSIONS: In the LCS-RP TKA, the contact point between the femoral component and polyethylene moved posteriorly under weight bearing condition, and the joint was more congruent and maximum flexion increased with weight bearing.

Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction Using an Outside-in Technique: Two- to Six-Year Clinical and Radiological Follow-up

PURPOSE: We evaluated the clinical and radiological outcomes of double-bundle anterior cruciate ligament (ACL) reconstruction using an outside-in technique with a follow-up of two- to six-years, especially in terms of the sports activity level and radiological degeneration. MATERIALS AND METHODS: Sixty-seven patients who were available for a minimum two-year follow-up after double-bundle ACL reconstruction using an outside-in technique were retrospectively evaluated. The mean follow-up period was 43.7 months. The knee function and stability were evaluated before the operation, one year after the operation (short-term follow-up), and more than two years after the operation (last follow-up). RESULTS: Regarding the knee function, the Lysholm score, International Knee Documentation Committee (IKDC) evaluation, and hop test showed significant improvement. Regarding the stability, the Lachman test, pivot shift test, KT-2000 arthrometer data, and anterior drawer radiographs using Telos showed significant improvement. Regarding the sports activity level, the patients who returned to pre-injury level activity was 68.7% according to the Tegner activity score and 76.1% according to the Cincinnati sports activity scale score. The incidence of aggravated degeneration or development of greater than IKDC grade A degeneration after surgery was 10.4%. CONCLUSIONS: Double-bundle ACL reconstruction using an outside-in technique showed favorable clinical and radiological outcomes with respect to the knee function and stability, joint degeneraion, and, especially, return to pre-injury sports activity.

Optimal Parameters for Sutures Tied to a Post during Anterior Cruciate Ligament Reconstruction: Thread Numbers, Knot Numbers, Suture Techniques and Stitch Numbers: An Experimental Laboratory Study Using Porcine Tendon / 대한스포츠의학회지

We evaluated the conditions required for sutures tied to a post for tibial fixation during anterior cruciate ligament (ACL) reconstruction. Harvested porcine tendon was used as a graft material and nonabsorbable suture was used for sutures. Samples were tested for ultimate tensile load and elongation according to thread numbers, knot numbers, suture techniques and stitch numbers. As thread numbers were increased, ultimate tensile load was increased and elongation was decreased. However, more than 4 strands of threads provided the sufficient ultimate tensile load more than 454 N of normal ACL for daily activities. As knot numbers were increased, ultimate tensile load was increased, but elongation was decreased. In terms of failure mode, unraveling occurred 100% in 3 and 4 knots, 81.2% in 5 knots, 54.5% in 6 knots, and 0% in 7 knots. Suture techniques and stitch numbers didn't significantly affect the ultimate tensile load and the elongation. For sutures tied to a post for tibial fixation in ACL reconstruction, more than 4 threads, more than 7 knots, and more than 4 stitches provide adequate ultimate tensile load and elongation.